10 Hafensauna - 25hours hotel Hamburg HafenCity
Perched right at the top of the hotel is the Hafensauna. Designed with fans of the traditional Finnish sauna in mind rather than modern-day spa-goers, it is a no-frills affair up on the sixth floor. There may sometimes be a stiff breeze, but great views are guaranteed. To cool off, guests simply step straight outside where they can look out over the port and the cruise ship terminal.
https://www.25hours-hotels.com/en/hotels/hamburg/hafencity