Nothing outside Tokyo's 24-Kaikan hotel hints at what goes on behind its gray concrete walls.

Tucked in a back street in Shinjuku 2-chome, the seven-story building could be an apartment block for retired civil servants. Only in the lobby, cheerily adorned with scenes from a sex movie, does it become clear this is one of Asia's biggest gay landmarks.

After passing the ticket machine — ¥2,600 for a 13-hour stay — pretty much anything goes, according to the guests, who come from across Japan and even abroad.