Are there swimwear days at the saunas and wellness centres?
This differs per location.
Arcen thermal baths has swimwear days in the saunas every Wednesday and every first weekend of the month. In the Arcen thermal baths, wearing swimwear is always mandatory, even if it's not a swimwear day.
De Parel Wellness & Beauty has a swimwear day every third Tuesday of the month until 5pm. There are special ladies' days and family days too.