Prime contender

Prominent beyond mention (in soaking sense) is the little town of Loutra Aidipsos (Edipsou / Edipsos) on the Greek island of Evia (Euboea) which is regarded as one of the nations premier hot spring resorts.

With this reputation comes a tad of tackiness: there's little the town can endear itself except a plethora of hot spring related / tourist business. 
And there's a lot of this, tripadvisor alone refers you to more than 100 accommodation options. Add to that a plethora of rental apartments. 
And you'll have to conclude that soaking is a way of life in Aidipsos.

Mint
And why is soaking so popular? 

One aspect would be it's vicinity to Athens. In a way it's far away from the capital yet not so poorly accessible especially figuring in the ferry after which it's just a 1,5 hours car drive to Athens.

Ferrying to the mainland, just half an hour but a step back from the hustle and bustle.

 
Then the number of hot springs themselves: 80 of Greece's 752 hot springs are located in Aidipsos according to wikipedia. Which is lot. So a lot of choice. Many are also on the seaside, so what better than have a peaceful holiday on the beach and soak at the same time? 
And with the visitor having a choice of where to stay and what soak to enjoy comes a distinctive turn away from the general Greek (Mediterranean?) penchant for medicinal soaking shunning the fun.

Then there's the historic edge. Matt has this:

'Edipsos is not a new phenomenon. Even though few travelers from other countries have never heard of  it the cosmopolitan atmosphere combined with the healing spas have attracted reknown politicians, artists, writers and other notable people like Winston Churchill, Aristotle Onnasis, Maria Callas, Greta Garbo and Omar Sharif. But it is mentioned in the works of Aristotle in his Meteorological, and by Ploutarch and Strabon. The town even minted its own coins. In Roman times the area flourished and its healing waters were visited by the emperors Hadrian, Septimus Severus and Marcus Aurilius. The baths from the Roman period are the best preserved and are known as Syllas Baths. During the Byzantine era it was destroyed for being an area of paganism though it was visited by the Emperors Theodosious and Constantine the Great'.

So well connected thus, historically speaking.

Disorder
It's quite obvious that soaking has always been an attraction here. And still is. 

Tripadvisor rates Aidopsos soaks with 4 stars (based on 55 reviews), mostly an average review from a diverse range of nationalities.  
Tripadvisor also ranks the hot springs as the number 5 of things to do on Evia island, itself the second largest island of Greece.

But let's look at more detail into the springs themselves. This website notes:

The hot springs of Edipsos are known since the ancient times. In the archaeological collection of the city, the visitor has the opportunity to see important ancient baths remains dating from the Hellenistic and Roman period. A large modern complex of hydrotherapy, including steam baths and Jacuzzi, operates in Edipsos. It has an outdoor Olympic-sized pool which waters come both from the hot springs and from the sea, as well as two indoor pools of thermal water. The hydrotherapy center does not have a hotel. Hence, the visitor must book their rooms in a lodging option in the area. These waters are said to treat acute and chronic rheumatism, arthritis deformities, espondilartritis, neuritis, sciatica, lumbago and injuries caused by ankylosis, gynecological disorders (salpingitis, endometrial infections, ovaries disorders, leucorreas and even some forms of infertility). Source: www.greeka.com

'The hot springs of Edipsos are known since the ancient times. In the archaeological collection of the city, the visitor has the opportunity to see important ancient baths remains dating from the Hellenistic and Roman period. A large modern complex of hydrotherapy, including steam baths and Jacuzzi, operates in Edipsos. It has an outdoor Olympic-sized pool which waters come both from the hot springs and from the sea, as well as two indoor pools of thermal water. The hydrotherapy center does not have a hotel. Hence, the visitor must book their rooms in a lodging option in the area. These waters are said to treat acute and chronic rheumatism, arthritis deformities, espondilartritis, neuritis, sciatica, lumbago and injuries caused by ankylosis, gynecological disorders (salpingitis, endometrial infections, ovaries disorders, leucorreas and even some forms of infertility)'.

The hot springs of Edipsos are known since the ancient times. In the archaeological collection of the city, the visitor has the opportunity to see important ancient baths remains dating from the Hellenistic and Roman period. A large modern complex of hydrotherapy, including steam baths and Jacuzzi, operates in Edipsos. It has an outdoor Olympic-sized pool which waters come both from the hot springs and from the sea, as well as two indoor pools of thermal water. The hydrotherapy center does not have a hotel. Hence, the visitor must book their rooms in a lodging option in the area. These waters are said to treat acute and chronic rheumatism, arthritis deformities, espondilartritis, neuritis, sciatica, lumbago and injuries caused by ankylosis, gynecological disorders (salpingitis, endometrial infections, ovaries disorders, leucorreas and even some forms of infertility). Source: www.greeka.com

The hot springs of Edipsos are known since the ancient times. In the archaeological collection of the city, the visitor has the opportunity to see important ancient baths remains dating from the Hellenistic and Roman period. A large modern complex of hydrotherapy, including steam baths and Jacuzzi, operates in Edipsos. It has an outdoor Olympic-sized pool which waters come both from the hot springs and from the sea, as well as two indoor pools of thermal water. The hydrotherapy center does not have a hotel. Hence, the visitor must book their rooms in a lodging option in the area. These waters are said to treat acute and chronic rheumatism, arthritis deformities, espondilartritis, neuritis, sciatica, lumbago and injuries caused by ankylosis, gynecological disorders (salpingitis, endometrial infections, ovaries disorders, leucorreas and even some forms of infertility). Source: www.greeka.com

Then there's this link:

'Edipsos is located at the green Northern part of Evia and is one of those unique places in Greece, where one can combine Natural Traditional Therapy, the latest in Thermal Spring Therapy with the beaches and atmosphere of a Greek island, the cosmopolitan atmosphere combined with the healing spas. There are more than 80 individual hot-water-springs ranging from 28 – 86 degrees centigrade, that can be very effective in curing problems like rheumatoid and inflammatory arthritis, spondylo- arthritis, tendonitis and many more'.

It's quite odd that most internet sites out there solely focus on attracting  the tourist; there seems little first-hand experiences.

Findings

We spent two nights in Aidipsos. I had banked on there being free and easily available seaside soaks, that much I had gleamed from internet. 

We arrived late the first day, spending a bit of time finding our digs even though the town plan seems very much straight forward (three long lanes running parallel to the long side of the beach cut through by small crossroads often). 

Along the beach itself is the main drag, mostly restaurants, not much to choose between. 

After dinner we move further to the cape, rounding it which passes the entry to the apparent gem of Loutra Aidipsos: the Thermae Sylla Spa & Wellness Hotel (photo below). It's regarded by some as one of the worlds premier spas (source):

'... one of the top 10 natural spas in the world, as voted by the prestigious Conde Nast Traveller [CNT] magazine'.

one of the top 10 natural spas in the world, as voted by the prestigious Conde Nast Traveller magazine - See more at: http://greece.greekreporter.com/2015/08/28/revitalize-yourself-in-greeces-hottest-spa-resort-in-edipsos-on-euboea-island/#sthash.RZUgkixU.dpuf

It actually was ranked fifth in 2011 in the Readers Awards of CNT category Medical, Thermal and Natural Spas.

 

Continuing: the road follows the cape and just beyond the hotel the beach gives way to 5-10m high cliffs. This would be where the soaks should be, but it seems in the closing of the day pretty much deserted (which in itself is a good sign for natural soaking) but also slightly eery. After the first cliff there's a bathing building which has been closed altogether and certainly has seen better times. There's precious little to soak in, just a trickle here and there. 

Surprisingly there's a building a block back on whose ground seems to give rise to many a hot spring. We circle the building the wrong way, around the back the going gets difficult in the dark. All very strange, back in the light of street we can follow an overflow along a bathing building (closed) and the waters disappear underground. 

How odd all. Are the springs all siphoned off for hotels? Even though there are not so many tourists (probably even less than there are soaks). 

Changes
The next morning we learn. The grounds on which the springs spring belong to the National Tourist Organisation. 

We must have missed the cave behind the building. Belonging to Sylla, wikivoyage has this:

'One of the surviving findings of the Roman period are the baths in "Cave of Sulla." The "cave" Sulla is a small building with a dome. The entire building is covered by deposits of sulfur waters that flow in the area and gives the impression of a cave entrance. At the entrance of the "cave" are two massive pedestals of statues with inscriptions in honor of the Roman Emperor Hadrian and Septimius Severus dedicated by the municipality Istieas. The first bear and later inscription in honor of Emperor Constantine of Byzantium. The "cave" was associated with the Roman general Sulla, who was visiting the spa treatment'.

 Around the corner the bathing building is noted as the

'... old spa of St. Anargyroi, a neoclassical architectural jewel gracing with his presence and reminds times when the resort of Edipsos dominated the Mediterranean'.

We do a similar swirl of town as the evening before. 

First it seems things have changed. Hot and sulphorous reeking water is flowing over the rocks  east of Sylla Spa. Has the tap been turned on (or off somewhere else?). 

Strange, but we conclude that the waters are hot and salty. Unfortunately the tide is in, so there are no appropriate pools to soak in: either boiling hot. Or cold.

Continuing onwards and today's discovery does certainly point to more waters as all along this shore waters are running over rocks and small culverts to sea. But nothing to really soak in. The famous sea based shower doesn't seem to be running either, so we leave it for today, not really over excited and look for a great alternative for today.

Looking back to the cape. The first cliff with a building on top, is what appears to be a shower (sometimes). The yellowish cliff has a couple of pools and in between are the deserted bathing facilities.

Dip

Is there anything else to Loutar Aidipsos? 

Well, the town's beaches are mediocre at best. Head over and beyond the bay for better or head along the south coast for more attractive settings.

There are also a hot spring nearby at Loutra Gialtron.

Head inland for some great scenery, some walks (I hope) but also visit the great Drimona waterfall (below), way up in the mountains. Very deserted on our visit it afforded us with delicious dip.

Snogged

 

Rich

The Azores and in particular the island of São Miguel are well-known for their volcanic origin. An origin which is still evident.

But it's especially the area in and around the village of Furnas, located in between the mountains on the east of São Miguel that really plays host as a geothermal hot spot.

From the wikipedia entry on Furnas:

'In the central part of the village, springs and geysers are prevalent; thirty springs, each of differing temperatures and chemical compositions, including warm iron-rich streams and piped examples of mineral-rich warm and cold water. The geysers are situated in several basins rich in sodium bicarbonate, boron, fluorine and traces of carbon dioxide'.

Maybe not on the same scale, it reminds one of Rotorua / Taupo (New Zealand), or certain areas of Iceland or the Italian island of Vulcano. And probably many more places on the globe yet to be witnessed by myself ...

I have no ambitions to make this the ultimate tourism reference entry to Furnas village, so suffice to say continuing reading this post you'll not be confronted with a never ending list of all what the village has on offer (and most of it being geothermal in origin).

Treats
But then again, there's quite a lot so I'll list what you should or shouldn't miss. Then continue with a soak at the Parque Terra Nostra and maybe in future a short entry on what's described (by those tourist PR persons) as a pool of paradise.

Anyway, nearly everybody enters the village from the west and after negotiating a curvy road over the watershed divide one suddenly arrives at the volcanic lake, Lagoa de Furnas. Walks are possible around the lake but note that on one side you'll be walking along the main road. 

At the far side of this lake is what is considered the main attraction of Furnas: a geothermal park with steaming and hissing pools, as well as boiling mud. Named Caldeiras da Lagoa das Furnas, visiting here requires an entrance fee which essentially is a labour programme; the fees are nothing exorbitant but cumbersome in all the administrative efforts which need to be met. Keeping a lot of people on the job. The site itself is ok, but nothing special. 

Much is made of the Furnas speciality for foodies: tossing everything in a pan and burying this pan to cook in the vicinity of the fumaroles. Named Cozido das Furnas (Furnas stew) it's not for vegetarians I believe ... 
Below is a photo of the various buried pots and hole's waiting for an upturn in tourism:

Continuing towards the village itself, you'll drop down over the side of the lake to Furnas which has an astonishing labyrinthal one-way system. Certainly for a village this size.

Listing
Things geothermal to look out for in / near the village:

• Caldeiras das Furnas, an area with many (22?) springs and fumaroles (photo below), just at the lower end of the village. Here's a little more info.

Note the nearby Observatorio Microbiano dos Acores. Tripadvisor gives this quaint institute / museum five stars. It is indeed worthwhile to walk through, note that they will even give you a full guide (speaking English) if required. Below an original tub from the termas.

 

• The Estação termal das Furnas (or as it's named now, the Furnas Boutique Hotel) is the hotel with access to it's own termae and is the official focal point of geothermal Furnas. Recently renovated it offers a number of "treatments" as well as possessing it's own indoor and outdoor pools with hot spring waters. Booking.com gives it a 9.2.

• Poça da Tia Silvina: a foot bath slash hot spring basin just upstream of the Boutique hotel just next to the river.

• Nascentes da Agua das Quenturas: a trio of springs opposite the Estação termal with each a different taste. Photo below:
  

• Banhos Férreos: a restaurant with indoor swimming pool with lukewarm but very iron laden waters. Even though the temperature of the spring is supposed to be 39°C (source). A meal here entitles you to a fee swim in the authentic pool. Tripadvisor notes just 3.5 stars. An experience of the soaking from tripadvisor:

  'Very relaxing, and not too hot, like some springs'.

  During my visit (photo below) it did not look like they were any takers ...:

 

• Praia de Fogo at nearby (7 km) Ribeira Quente. Rumor (?) has it that there are under water hot springs making this Fire Beach a little warmer than the ocean. Not noticeable on my visit, possibly due to wrong timing (come at low tide?)

Full info on all the features including other attractions of Furnas can be garnered from this government website.

 
Revelations

With this out of our way let's continuing with the hot spring of Parque Terra Nostra (Our Land) which is not your typical geothermal soak. 

It's located within a park, under the gaze of historical residence. 

The park itself is a haven for plants which enjoy the milder weather and high fertility of the soils. 

On a side track, did you know that Furnas is one of the few (if even there are others) where the taro plant is grown commercially in Europe? Back when I was a bit younger, my first job as an agriculture specialist was to assess taro plants in the South Pacific. It's very appealing to observe taro fields under irrigated circumstances (as in Furnas), similar to rice.

Anyway historically the residence and pond were first part of the residence of the honorary US consul of São Miguel back in the times when the waters around the Azores were teeming with whales. With the demise of the whales (thank you) the property reverted to Portuguese gentry control which expanded the park and buildings. However early last century neglect crept in only to be revived shortly before World War II; a period which also saw the hot spring pond expanded and sourced from hot spring water.

Parque Terra Nostra entrance

It's unclear where exact the springs itself source from. On the far side of this pond are two powerful spouts which seem the sole source of the geothermal waters. The pond is quite large, 50m in circumflex with still warm waters, depth would be around a meter and half.

We arrived late afternoon, an hour before closing time. It's a six euro entry fee. A 100m further one comes to the pond. To your left over the edge of the pond and sheltered within the greenery are a number of changing rooms, seeing brisk business this (Sunday) afternoon. 
A quick change and up to pool side. 
The orange tinted waters are warm, but not hot. One can drift around though setting up camp near the spouts ensures a warmer soak.

 

The change rooms revealed (not literally) that it's quite busy even though it's out of season. Many a tour group wander in and around.

What I do notice is the absence of showers. There was one, but didn't get used, though many a tourist changed poolside (discreetly, this is Portugal) so it's only guessing what the waters are like. This large body of water will not be flushed easily. Is this aspect underestimated?

Showers by the way would help post soaking, as the waters taint the lighter coloured bathing costumes a shade of orange.

No, no smell.

So not positive? Well, the large body of water gives enough private space and the greenery around makes it highly recommendable. It's an enjoyable way to end a day's visit to Furnas and surroundings.  

 

Spouts on the far side

 

Wear and tear
There's a hotel attached to the park  which is owned by the company named BenSaude. Booking.com gives this hotel an impressive 9.3; note hotel guests have access to pool beyond closing times for others ...

Other experiences are very positive. Tripadvisor notes 4.5 stars (400+ reviews), the no. 2 thing to do in Furnas. Extracts:

'The changing facilities are not great and I only found one outdoor shower but the experience is great'.

'I'd recommend wearing an older bathing suit as my light coloured bathing suit was stained even after washing it the same day'.

A lot of these reviews though are very recent which begs the question has there been a sudden influx of tourists? Due possibly to cheap flights (Ryanair / Easyjet)?

Finally, there's not much original experiences on the internet, it's mostly photo's. An exception, the Daily Telegraph (Mar 23, 2011) has an article which in it's first half describes a sojourn in Furnas. An excerpt on Terra Nostra:

'It is the Portuguese equivalent of Iceland's Blue Lagoon, a hot, murky lake with steam rising from it, fed by a geothermal spring and filled with bathers taking to the waters in pursuit of health, happiness and surreptitious snogging.

There the comparison ends, since this thermal pool in Furnas, on the island of Sao Miguel in the Azores, is muddy brown because of iron in the water and dyes your toenails orange, while the backdrop is not the Svartsengi power plant but the palms, ferns and conifers of a subtropical Atlantic forest'.

Hidden

It had been a tiring day, leaving Reykjavik early, heading through the snow eastwards along the south coast of the island. The further eastwards we got the deeper the snow was. Past Skógar we stopped at a few places, taking sideroads through the virgin snow and also went up Solheimajökull glacier, not with the expected cramp-ons, but with snow shoes so as to deal with all the fresh snow. It had been the best of snow of the season they said. After catching our breath, we headed to Skógafoss and as the heavens closed there was still the need to visit to hot spring.

The hot spring of Seljavallalaug is up a valley heading towards the  Eyjafjallajökull mountain.  From Iceland's highway 1, it's an easy 5 kms up side road 242. Continue as far as possible to where there's a small car park. From here it's a 15 minute walk upstream to Seljavallalaug, which is hidden from those heading there, behind a cliff.

Where art thou? 

The path is obscured by the now slowly falling snow. There are still a few persons returning, but we seem to be the only ones heading the other way and  intending a real winter soak. The path scrambles over some flat scree (?) and past a rock strewn side valley which also entails a jump or two over a small stream to reach the other side.

After this crossing, one skirts a big rock cliff and wanders along the pool and can feel the heat from the source at this end. At the far end, the changing rooms are empty save for some refuse. A quick strip and a jump into Seljavallalaug.

Looking south, from the changing rooms, the hot spring is at the far end.

What I hadn't read was that the waters were just 30 degrees, meaning a lot cooler than expected! A quick length is made to the heat source at the other end, but Seljavallalaug is something more to be savoured in summer ...

Lessons learnt

Originally the bassin at Seljavallalaug was constructed so as to afford swimming lessons. Snaeland & Sigurbjörnsdóttir (2010) add that construction took place in 1923 and the pool size is 28 by 10m. 
If one follows the link to this photo of those first swimming lesson days group shot. 

More history:

'A local man, Björn J. Andrésson, had been appointed to teach sports and swimming. He decided that a swimming pool should be built above the farm of Seljavellir, where geothermal springs flowed from the rock. He gained the support of local farmers, promising them free swimming lessons when the pool was completed. Twenty-five men took part in the task.
The original Seljavellir pool was built of traditional Icelandic construction materials, rock and turf, in 1922.  Nine metres long and 4-5 metres wide, the original pool took two days to build. Swimming lessons were due to commence three days later. Twenty-five people were registered for the first swimming/sports course, during which they camped at the swimming pool in tents.
The swimming pool was such a resounding success that the following year a larger concrete pool was built on the site, inventively constructed using the rock face as one side of the pool. It was the largest swimming pool in Iceland at the time'.

The changing rooms: a little tired?

Since the nineties it's role of catering to summer guests swimming needs has been take over by a more recent construction, downstream. Volunteers though have been maintaining the facilities, but there is only so much they can do. Once a year the whole pool is scrubbed down, so it's hoped that the current users have the sensibility to not pollute the waters. Or the changing rooms.

As Seljavallalaug lies at the foot of Eyjafjallajökull, after the 2010 eruption, these volunteers took great efforts to empty the pool (photo).

Privilege

Once more Seljavallalaug is also rated as one of Iceland's best hot springs (source). Britain's Guardian (20 July 2013) also rates Seljavallalaug in it's 10 of the world's best swimming pools:

'At the bottom end of the valley, the amazing Seljavallalaug geothermal pool was built in 1923, making it the oldest in Iceland; and it was its largest until 1936. It is now partially filled in with the ash of the 2010 eruption of Eyjafjallajökull but the scenery is fantastic and the water naturally nice and warm'.

Seljavallalaug gets four and a half stars from Tripadvisor which is not too bad for a natural attraction with only the visiting public needing to maintain the site itself.

 

A good blog entry on Seljavallalaug comes from the wonderful unknown:

'I've been having doubts about sharing the Seljavallalaug swimming pool. Although it's very close to the Ring Road where thousands of tourists pass every day towards the nearby Skógarfoss waterfall, nobody seems to know it. Except the locals and a few foreigners. And that's a good thing because the atmosphere around this pool is created by it's solitude. We've had the privilege to enjoy it all by ourselves with the surrounding mountains as our only companion and it wouldn't be the same when crowded.' 

Another nice entry comes from iheartreykjavik which also has more background on the need for swimming instructions back then.

Finally, here's a video of Seljavallalaug.

Note:
Snaeland, J.G. & Þ. Sigurbjörnsdóttir (2010) Thermal pools in Iceland. Skrudda, Reykjavik, Iceland

  

The return journey