24 Kaikan Shinjuku is a popular gay sauna and Tokyo's biggest cruising spot for gay men.
With 8 floors, the 24 Kaikan Shinjuku features a dry sauna, steam room, jacuzzi, solarium, video room, private cabins, snack room, lockers. The rooftop floor has tanning beds and a cold bathtub. Cabins are expensive, so actions take place in the common areas.
Foreigners are welcome (your passport may be required). Remove your shoes and change into slippers. Purchase a ticket from the vending machine and give it the front desk. You'll receive a key and a bag with a robe and a towel.
Rooms for rent are available. Open 24 hours a day, 7 days a week. 24-Kaikan has two other branches in Ueno and Asakusa.