A gay sauna in Tokyo can be found mainly in and around Shinjuku Ni-chome. The most famous house is the 24 Kaikan, which is spread over several floors and is open around the clock. In addition, there are other saunas and so-called Hattenba, i.e. cruising establishments, some of which are aimed at a specific audience. While some hotels focus more on relaxation with a bathroom and relaxation areas, others are clearly about cruising. Because many things are centrally located in Ni-chome, a visit to the sauna can be easily combined with an evening in the bars.
A few things are different in Tokyo than in Europe. Tattoos are not welcome in some houses, this has historical reasons and is not a value judgment, if in doubt, ask beforehand. English is not spoken everywhere, but you can usually get by in the saunas around Ni-chome. You can usually get a towel and locker on site. Depending on the house and the time of day, the prices vary. Because some saunas have fixed days with a special programme, it is worth taking a look at theme evenings. If you go to a sauna for the first time in Japan, you should briefly inform yourself about the local customs, then the visit will be relaxed. The following addresses will show you which house suits your evening.