Is it true that new houses are constructed/architectured as "sauna first" and then everything else is planned around the sauna?
or is that just an urban legend claim?
I have no idea if that claim is true, but what I did love about visiting Finland was the even the small apartment I rented had a sauna in it! It seems like it's a non-negotiable for even the smallest accommodations.
While it's true something like 90% of the accomodation have a sauna it's not like everything is planned around it. It's more like that it's the ONLY well soundproofed space, with nice atmosphere, that makes life enjoyable when your neighbors suck.
Trust your instincts.
Not around the sauna per se, but sauna is often built first because it serves as a place to live while you're building the house!