Although hardcore street skaters may scoff at the idea of an indoor park as the best place to skate in a city filled with steps, rails and the usually dry River des Peres, the multilevel warehouse known as Ramp Riders, with its excellent plywood half-pipes, bowls and BMX jumps, is the ideal space for practicing your ollies, impossibles, sex changes, fakies, grinds and 360's. Even the pipes and debris in this seriously gritty warehouse, buried in an Midtown industrial area -- think of a post-tornado City Museum -- become stunt props for maniacs. Ramp Riders offers Monday beginner sessions, but the rest of the week is open for skating to everyone over twelve. Don't worry, Mom -- helmets are mandatory and kids under eighteen must have a parent or guardian sign an insurance waiver. A lounge sells junk food, and on the TV is -- what else? -- skate videos. But best of all, at Ramp Riders the cops can't touch you.