washington park my man. people will bitch at you for riding the trails, but you can make laps pretty well. take the max from downtown to the zoo station, get off and your pretty close to the top. if you know the right way down, you will find yourself at the bottom max station again.
also, there is a sick setup hidden in the woods. some guys have put together some nice drops and hits. however, i didn't build it so i can't tell you exactly where it is. these guys put a lot of effort into it. however, starting at the elephant house road switch back is a good place to start if you want to find the hits.
I hope that some day we will be able to put away our fears and prejudices and just laugh at people