The low key alternative 20km from Loutra Edipsou!
We found this place by accident browsing Google Maps, so we had to come and find it. Dip it. There is a defunct bath house with individual tubs across the street. The pool at the sea was just recently formed by a tourist who wanted to bath there. So by the time you get there you might want to bring a shovel in case the sea has pulled it apart. There is also a second pipe bringing a smaller amount of water just 10m next to this one.
Gialtron baths, Evia, Greece: It's a low key free hot bath at the calm bay in a village. Amazing if your nearby, but not worth a long travel either. – bert