"Oh no, the sauna is closed."
Translation:Voi ei, sauna on kiinni.
I agree with everything above. A detached house without a sauna is very rare indeed, but small apartments don't necessarily have one. Older apartment buildings (1950's, 1960's for example) are very likely to have a common sauna where your can reserve your own slot. Some very recent apartment buildings might have neither private nor common saunas, but that's a new trend and I'm not sure it will continue. There were a few decades when almost no communal spaces were being included, but now that people are adding gyms and club rooms to apartment buildings, common saunas might make a comeback.
And of course, there are summer cottages/holiday homes/grandma's old place in the countryside where no one lives anymore. Finns love escaping to those in the summer, there's approximately one for every ten Finns, and I don't think I've ever heard of a summer cottage without a sauna.
In "own" house, it is very common to have sauna. In apartment houses or row houses you might have your own sauna or there might be a common one (usually you have a dedicated time to go there, so no "random" people with you :) ). However it is not mandatory (as I would assume air conditioning in Florida) and for example I don't have a sauna. I estimate that this is rare, let's say under 10% (no citation).
We also have commercial saunas, commonly in sport places like swimming hall, gym etc.