Also while 73°C is a proper sauna, there are plenty of hotter ones. 90°C is closer to what I'm used to at my apartment building's common sauna. I do take two breaks when I'm there for 30 mims though.
It's a sauna so humidity depends on how much water I feel like throwing on the stones ("kiuas"). I throw at about once per minute, but I have no idea what that would mean in humidity.