sauna

Short definition from Wiktionary

Noun

1. 1
   A room or a house designed for heat sessions.
2. 2
   The act of using a sauna.
3. 3
   A public sauna.
4. 4
   In some countries, a business with bath-like facilities that is actually a brothel or a place for (non-commercial) sexual encounters; a bathhouse or massage parlour.
5. 5
   A very hot place or room.

Verb

1. 1
   To use a sauna.