[weberer]

The cheaper apartments tend to not have private saunas built into the bathroom, but most apartment complexes at least have a shared sauna on the top floor. Residents can book a block of personal time in advance.

[httpsterio]

In most buildings the shared sauna is on the first floor (basement) and not top.

[euroderf]

Also there can be blocks of time regularly scheduled, for example on weekends.