I am always on the lookout for natural half pipes: streets that go down a steep hill and then straight back up another hill. For roadboarding and bicycling, it's my favorite; going up and down, up and down, with minimal effort. So the idea is to build a massive park, initially one half pipe, that was maybe 100 feet long, 30 feet high. I don't know the physics, but you get the idea, insane speed. Not neccesarily going airborn, just tracing beautiful weightless arcs, 25 feet up, on a...