How to build a Finnish bathhouse?

The Finnish bath is distinguished by dry steam, its temperature can be 120 degrees. In Finland, every third inhabitant of the country has a home sauna, however, now, of course, few people drown them with firewood, they have been replaced by electric heaps, they can be put, in principle, to any place, so the sauna does not have to be a separate building , it can be built into an existing room, it is not necessary to build it, starting from the foundation. The temperature regime in it can be adjusted automatically.