Dude! There is nothing cheaper than free, and free is one concept that truly befits the sport of skateboarding, which, at its best, has no rules -- except, perhaps, those agreed upon by the boarders themselves. And that's exactly how things work at this 60,000-square-foot, city-built facility, which opened to the public in summer 2001 and has been such a hit that it's already expanding. But the fun at Denver Skatepark isn't reserved just for the kids who cram the place: Watching the action can be every bit as entertaining. Grab a soda and hot dog from the cart that always seems to be there when the boarders are, find a spot with good sightlines of the concrete bowls and ramps, and prepare to be amazed -- and amused.