Thalassotherapy comes from the Greek word thalassos, or sea, and is a treatment system using fresh heated seawater which induces an exchange of minerals and toxins between the blood and the water. It is extremely popular in Europe, especially France.
As with thermal spas, thalassotherapy centres benefit those with certain medical conditions such as arthritis, and also those without. Typically, a stay at a thalassotherapy centre would include daily bathing in a heated seawater pool with jets, and other facilities such as as massages, aromatherapy or algae wraps.
Euros are very big on water spas and resorts - we spent a day at one in northern Italy, and it was pretty cool. We did not participate in any algae wraps.