Sworn

Usage of seaweed in a hot bath seems a no-brawnier. 

We all know the the benefits of bathing in heat. And the many qualities of seaweed are also well-known (source).

But somehow a seaweed bath has never become a common method of bathing. 
Other than in Ireland. 

And even here, it's seen as a novelty, something that is just surviving the changing times.

It was not always like this. On the extensive (and excellent) Irish website The Seaweed Site it has a section on seaweed baths:

'Seaweed baths are popular in Ireland, but are not a recent phenomenon as many date from Edwardian times, when they were more widespread than they are now. There were baths in most large seaside town such as Salthill, Co. Galway, and Howth, Co. Dublin. Essentially, seaweed baths are ordinary baths (usually for one person in a private room) filled with hot seawater and seaweed, generally wracks such as Fucus serratus. The wrack is generally steam-treated prior to use so that it releases minerals, trace elements, and polysaccharides such as alginates.Many people swear by the efficacy of seaweed baths in the treatment of rheumatism and arthritis'.

The website of Voya (seaweed based cosmetics and baths) adds:

'Seaweed bathing is a 300-year-old tradition and Ireland's only indigenous therapy.
...
The therapeutic properties of wild seaweed have long been known along the Irish coast. At the beginning of the 20th century there were an estimated 300 seaweed bath houses in Ireland and nine in the small town of Strandhill alone.
...
As a tradition, it had seen a significant decline due to population shift away from the Atlantic Coast, and the rise in non-Organic treatments'.

However, in recent times Ireland has seen a renewed interest in running the seaweed baths and taking a bath as a form of recreation. And as a beauty treatment.

The Irish Times (Jul. 26, 2005):

'The Irish seaweed industry has effectively doubled in the last five years and is worth €12 million per annum and employs more than 200 people full time and about 200 people part-time. While most of the seaweed harvested every year is exported for food and agriculture the health and cosmetic side of the industry is developing at home.The niche market of traditional sea baths and the continental-style thalassotherapy spas (thalassotherapy is the use of seaweed or seaweed extracts in health or beauty treatments) is ripe for expansion, says Guiry [director of the Martin Ryan Marine Science Institute at NUIG]'.

I've tried to explore whether or not bathing with seaweed has a wider appeal in the world.
It's quite difficult. 
One of the few I've discovered are the Reykhólar Seabaths on Iceland. From this blog, last year:

'It's a very interesting concept, find more info at sjavarsmidjan.is. Icelandmagazine (Jun. 7, 2016) has an article on the same: 'Landowners in the small village of Reykhólar, in the South Westfjords on the north coast of Breiðafjörður bay, are planning to construct a large geothermally heated seaweed spa and bath, offering travelers the opportunity to relax in warm water by the edge of the water'.

One reason for the lack of additional non-Irish finds lies partially in the difference between seaweed and algae. Basically algae are a much larger group of which seaweed is part of. See differencebetween.com:

'What is the difference between Seaweed and Algae?· Seaweeds are a group of algae, and have some special characteristics viz. macroscopic, multi-cellular, benthic, and marine.· Diversity of algae is extremely high and incomparable with that of seaweeds.· Algae could be both unicellular and multi-cellular, whereas seaweeds are necessarily multi-cellular.· All the seaweed species are autotrophic, whereas some algal species rely on other external food materials.· Algae inhabit both freshwater and marine waters, while seaweeds inhabit only seawaters.· Marine algae can distribute over shallow as well as deep waters, while seaweeds mostly inhabit shallow waters'.

But though the above may be clear, in non-English there's less to distinguish. In French f.i. both are algae. But even then there are precious few signs that seaweed bathing takes place elsewhere, with possible exception of Japan. Beats me. Why aren't there more similar experiences possible in other countries with seaweed in abundance? Canada, Norway, New Zealand, Chile, etc. ?

Wracked

As it was to be raining all day, we decided to pay a visit to what might be one of the most prominent seaweed bath establishments in Ireland, that of Voya at Strandhill, a couple kms outbound from Sligo town, oceanwards. 

Even though it was a weekday during February, rainy and a hefty wind whipping up the normally surfable waves of Strandhill, the seaside village seemed to be doing good business. 

I couldn't discover where these visitors were, there wasn't much bizniz open. And at Voya Seaweed Baths we were assisted promptly.

The reception area is quite the upmarket beauty reception: nice ladies, lots of seaweed based cremes and assorted in view, but the whole process of inquiring and subsequent intro to the bathing process was very efficient and sincere.

For 55€ (and after 5 minutes wait), the two of us were lead to a room with two larger bath tubs, half filled with steaming water in which a bunch of seaweed is floating. 

In the corner there's a small steambath. Apparently steaming first assists the whole bathing process by pre-opening the skin pores. 

The whole procedure of undressing and redressing, steaming and bathing should take no more than 50 minutes. Even then, it's all very relaxing. 
The seaweeds are encouraged to use as a sponge so as to leave oily films on your skin.

katodunne on how the Voya experience looks likes:

Mmm @voyabeauty@something__memorable

If I'm not mistaken, Voya Seaweed Baths uses what they call Serrated Wrack (Fucus serratus) organically certified and hand collected nearby. From the wikipedia site noted I learn that this seaweed is home to Northern Atlantic shores. But I'm still wondering why bathing with seaweed is not more common.

Wishing
A couple of other experiences, not necessarily  from Strandhill. 

The BBC (20 Oct. 2014):

'Sporleder averted his attention to photographing the experience while I changed into a bathing suit [?]. Climbing into the tub, I slid my body underneath the tangled seaweed and reclined. I pulled the oily strands between my fingers, added some hot water to the tub, and rubbed the flora into my skin.Once Sporleder was finished photographing, we alternated between the cedar wood sauna – a box that left only my head exposed – and the old-fashioned, brass-tapped tubs. The steam inside the box opened our pores to the biting Irish air, and the bath infused the seaweed oils right into our skin. The treatment is supposed to be followed by a cold shower – but I’m a Canadian who’s against being chilly'.

There's an article from the Guardian (12 Jan. 2013):

'We are sharing a cubicle at Kilcullen's Seaweed Baths (kilcullenseaweedbaths.com) on the edge of Enniscrone beach in County Sligo, north-west Ireland. I'm in a huge, ancient cast iron bath with crackled cream enamel, and I've decided to float on my back in the green water, piling the huge mounds of luscious fleshy seaweed all over me. I float easily in this salty hot water, and, as I close my eyes and breathe through the steamy fronds, I, too, feel like I'm on drugs'.

Piquenewsmagazine (Sep. 21, 2017):

'However, they tweaked the experience to provide something more upscale than the communal bathing of yore. At Voya, I have a private room of about 5 x 10 feet (1.5 x 3 metres). The walls are brown granite squares, one with a Celtic design, for an understated Irish theme. An attendant advises me to spend five minutes in my private steam room before entering the tub. I've also been briefed to soak my hair in the seaweed bath, and not to rinse it afterwards. My entire session will last 50 minutes.Thoroughly steamed, I climb in the bathtub and pull mats of seaweed over my chest. Fortunately, nothing swims out. The smell is mild, and the concept feels only slightly weird. A shelf by my head holds a lit candle, a pitcher of water and a cup. I entertain myself by taking seaweed selfies and wishing my arms were longer'.