Hmm, not sure if i'm riding "legally" or not.. but there is a place really, really close to my house. I only have to walk the bike across one road to get to it, and then ride down a vacant road and boom: riding paradise. Its at the end of (location removed to protect all involved). Its a toxic waste dump to the right, but surrounding it are just acres upon acres of trails and a decent track as well. But the best part is the trails.. miles and miles of trails that intertwine and interwine and just seem to go on forever.
But before we found this, we would always ride on vacant land, farms, and construction sites. Some of my friends are dumbasses though and mess it up for the rest of us by riding too close to houses, roosting on lawns, racing cars on the street, or the worst: running if the cops come. Seriously, if a cop ever comes I always just stop and talk to them like a responsible young adult. They either tell me to go home, or keep riding until they get an official complaint. But any time I hear a kid whining he got his bike impounded, its because he decided to run from them.