Downhill

We of course focus on terrestrial hot springs, but forget not there are naturally many sub-marine hot springs (most unknown). 

And then there are those thermal springs near the shoreline. 

Milos (Greece; various: Aliki, Paleochori, Skinopi and Tria Pigadia) Termas da Ferraria (Azores, Portugal), Vulcano (Sicily, Italy) and Pantelleria (Nicà) are islands visited which have hot water sources close to / just beyond the tide marks. Elsewhere on our fragile planet, what comes to mind are Ikaria (Greece), on the US / Mexican west coast, Eastern Russia, Japan and NZ which have hot springs close to / on the shore. And probably many more locations likewise.

So not so unique that the Isle of Ischia (Bay of Naples, southern Italy) has a hot spring right on the tide mark.

Ischia's origin's are very much geo-tectonic and volcanic, even though the last eruption was 700 years ago. The island has always been known for it's geothermal sources, much of it's current touristic popularity is due to the abundance of hot springs and it's attraction to (mostly) German and Italian visitors.

Alas, virtually all of these hot springs are hosted by a commercial exploitation, mostly in the form of resorts with many pools / restaurants and rooms.

An exception to the commercial exploitation of the islands natural resources is the hot spring of Sorgeto.

Sorgeto is located in the southwest corner of the island, at the top of a small bay. Surrounded by steep hills, it's fair way walking down from the roadside (from Panza), even more strenuous walking back. Authorities have built a walkway / stairway down (250 steps, link. Or 300?) and there are two businesses close to the shore providing services to the visitors.

One of these, the La Sorgente restaurant facility (3.9 stars rating by Google) takes a large bite out of the little shoreline, though if you remain east of this, there are some small steps where many soaker takes to the water. 

Note to enjoyment. Sorgeto is very popular: many visitors report (warning!) that Sorgeto becomes packed from mid-morning until sundown, even more so in the weekends. And just as a side note: Andrea Bocelli comes here often and recently (source).

On my first visit, there was quite a lot of wave action, making usage of the springs from the sea bed quite difficult, even though there are ropes to hold on. 

On the west side of the bay beyond the facilities there are more opportunities, though these are even less sheltered, so the sea really needs to be a lot calmer.

Under the cliff (that's to your left, facing the sea) there is a cave with very hot springs inside. During my visits there was a makeshift barrier, not very effective on keeping visitors out from here.

Reviews? 

Tripadvisor (4.5 stars from 70+ reviews) and Google (likewise 4.5 stars but from 6.000+(!) reviews) seem to agree.

Scalded

More info. 

From the Wikipedia Sorgeto Italian page. Translated:

'The bay is characterized by the presence of hot and mineral springs, saunas and therapeutic steams. It has a moon shape surrounded by vertical rock walls, it is divided into stone basins where the thermal water flows, which flows from underground at a temperature of 90°C. The thermal waters communicate directly with the sea, thus creating a single area in which fresh and salt water, hot and cold, meet.

Initially unknown to the mass of tourists, also due to its difficult access, in fact, it is necessary to descend about 200 steps, today the bay is among the symbolic places of the hamlet and of the entire island'.

Wikipedia also notes that the area was once inhabited by Greeks (roundabout 8th century BC).

A couple of selected other sites on Sorgeto and the Sorgeto experience.

Lonely Planet:

'Among all those posh, dreamy (sometimes expensive) spas, it's nice to have access to something that's thermal and free. Located at the bottom of 300 steps, 2km south of the village of Panza, hot thermal water spills into rock pools on the edge of a secluded bay, where it is tempered by the chill of the sea. Choose a spot with an optimum temperature (careful – the water can be scalding), lie back on a rock and luxuriate.

There's a scruffy kiosk at the cove that's only open in the summer.

The cove can also be reached by water taxi from Sant'Angelo (€5 one way)'.

Solosophie has a blog entry (updated March 11, 2024):

'The sea cove itself is blessed with outdoor natural thermal waters which are akin to lying in a bathtub and are a reward in of itself for those who hike down the stairs to reach the inlet. In times gone by, islanders would have used the thermal waters closest to the shore to cook eggs and the like'.

Ischiainsider on the "free" hot springs on the island. These being the Fumaroles and Sorgeto: 

'Sorgeto is a small bay with rocks, pebbles, and pools of hot water. There are vents of hot spring water that come up through the sea floor, mixing with the cooler salt water to form warm currents and pools among the coastal rocks with temperatures between 30 and 37 degrees'.

Terme.Ischia.it:

'Sorgeto is an inlet with pebbles and thermal springs. Be careful not to scald yourself on the water line! This beach is accessible from the centre of Panza via a street that is approximately 1 km long, on foot or by car. From Sant’Angelo one can reach the beach with the convenient taxi boat. Sorgeto is a cove, the location of a true, outdoor thermal park. Boiling fountains and minerals, saunas and therapeutic vapors, this is what Mother Nature wanted to give the island of Ischia in remote times and today it is available for free for all those who are looking for a place to reinvigorate themselves from the daily stress and hardships. It is accessible both by sea and on foot via a steep ramp of stairs that leave from the village of Panza. It is a true relief to let oneself go to that mixture of warm-cold, sweet salt water and to taste one of the most marvelous sunsets that one could ever image. Be careful, though! Its rocks and stones are at times boiling hot! In one of the little basins from which the waters bubble, the islanders cook eggs, potatoes and seafood, a custom that most certainly is repeated century by century as is evidenced by archeological finds discovered in the zone. The most fascinating characteristic of Sorgeto is bathing at night on the warm under the stars. One can relax as one spends unforgettable moments here. The mild temperatures are present here even in the winter and therefore allow for one to tan and bathe even in the coldest weather!

Thermalsprings.ru has a section on hot springs near Sant'Angelo.

Bubbles

You can walk from Sorgeto to the picturesque town of Sant'Angelo (about an hour), though the path is far from obvious. 

Eastwards from Sant'Angelo, once the coastal path hits the beach, there are a number of subterranean fumaroles. Shuffle your feet in the sand for warmth, but note that it gets hot quickly.

Ischia.it puts it as follows:

'Just a short walk from S. Angelo and the thermal gardens Aphrodite Apollon, on one of the most warm thermal flanks of the island, in a small section of Maronti, spew for centuries the breath of Tifeo from the depths of the ground. This is a most interesting phenomenon resulting from the volcanic activity of Ischia: the Fumarole. From the ground in this area a great thermal energy emanates and produces clouds of vapour in the external atmosphere and bubbles of gas in the ocean at about 100°C, observable with a submarine mask a few meters from the shore.
Since the times of Romans, the warm sand was used to cure body pains through sand-baths a pallet is dug with one's hands, one lies down and covers the whole body with sand, leaving only the head out. Over the course of the centuries these thermal waters had many uses, the heat being used even for culinary needs'.

A Final parting note.

The bay of Sorgeto is forms part of the Area Marina Protetta Regno di Nettuno, a marine park encompassing Ischia's coast as well as that of nearby Procida.