Paris's newest blockbuster gay circus occurs only on Friday and Saturday nights, within one of the many cellars beneath the city's tallest building, La Tour Montparnasse. Inside, you'll find two separate dance floors divided by a wide hallway, each with its own bars and sound system. A clientele of up to 2,500 mostly gay men, aged 18 to their late 30s, roils and mingles restlessly between the two rooms, where house and techno reigns, and where specific evenings might be themed after prominent gay bars in, say, Ibiza or London. Don't even think of arriving early; hours are almost defiantly late.