That is one hot dry sauna
A few steps up from the Ma’in Hot Spring is a cave. The inside is sweltering hot. The water on the ground is so hot that you cannot step in it. I did. And I scowled and jumped back immediately. There are mats laid there where you can step on and sit on the rocks.
I have not yet figured out what the rich green coloration comes from. They are not algae/lichen etc. It is too hot for that. That is the color of the rock itself. Perhaps copper oxide?