Someone recommended stone spa - ganbanyoku (岩盤浴) to me a long time ago. She said that you laid on hot stones, and all the toxins and bad stuff was pulled out of your body and into the rock. Stuff like nicotine, additives, etc.
Then this girl wrote about it. And my friend T. was coming to town and I wanted to take her to do something interesting that you don't have to get fully naked for.
I sussed out a shop in my area using this site, and one torrential Monday night, we three girls checked in to Air Api, which also has a hot yoga studio. We checked in and filled out a short membership form, and a staff person gave us a short how-to chat. Then we were given a bag with towels, pajama-like getups, and bottles of water. We stripped off our skivvies in the locker room and changed into the sweat suits, then went into the stone spa.
There were several different kinds of "beds", made from different kinds of rocks; some in slabs, some beds of loose rocks. They each purported to address different bodily ills: metabolism, cancer, circulation, and so on.
There were two rooms with different degrees of heat, as well as a "cool-down" room for, well, chilling out between sessions.
After the second ten-minute round, the sweat really started pouring out. The room was filled with slick, glowing women (men can do it too, but it's sex-segregated). At the end of our 90 minute session (¥1000), we showered and went out into the street, feeling refreshed and clean and pretty awesome.
It's like a sauna, but I liked it better, probably because of the poshness and the relaxing atmosphere. I always get bored in saunas, and hot really fast. In this setting, you can stretch out and relax and be alone with your thoughts. There's no talking inside, so you can just lie there and think and perspire.