Do you have to have membership to go here?

Nope

Are teenagers allowed?

You can go parilka (sauna) any time, however, spa requires booking in advance. No membership, but bulk pass is more affordable. They also offer gift cards.

You do not need a membership. To use the spa (wet sauna, dry sauna, cold pool, salt pool and hot tub) you can pay for a single time, or buy passes that give you 5 visits for the price of 4

No memberships, but please don't bring young kids :/