Here is one of the sweat lodges at Apache Springs Camp. In the center is a hole in the ground. You first build a giant fire using lumber yard scraps provided for the purpose. You put chunks of lava rock into the fire until they are red hot. A group then enters the lodge and sits around the edge. The staff fills a bucket with the hot rocks, puts it into the hole in the floor, and closes the door. You have a bucket of water, which you slowly ladle over the rocks to produce steam. This, of course, makes you sweat profusely.
When you don't get any more steam, you leave the lodge and dump a bucket or two of cold water over yourself. It's better than a hot shower!
This picture was taken on Troop 104's 1994 trek to Philmont.