Ben Mullinkosson is a film-maker and skateboarder from Chicago who brings an effortless, freewheeling intimacy to this immersive and sensual study of the underground club scene in Chengdu in central China. The title is enigmatic, but it seems to refer to the imminent closure of a club called Funky Town where his subjects have been hanging out; the darkness is the club’s darkness, which is enfolding and welcoming and reassuring, a neon-detailed night in which nothing matters but youth, beauty and the pleasure of the moment. Mullinkosson is utterly at…