A big sauna with a huge window looking out on the forest and the outdoor hot tub that's big enough for many people to warm up from the cold. This could also be used as a cold pool for dunking after sweating in the sauna.
A 'real' sauna. They're the ultimate escape & pitch black inside, except for the tiny slit of light pouring through the opening where steam escapes. The experience is not about fashion, design, or even beauty. It's primal and it's about the soul.