It's a little tricky to find. If you're going south on Interstate 35E, take Illinois Avenue west about two miles to Pierce and hang a left (south) less than half a mile past the houses. Turn toward a parking lot at the back of an apartment complex and you'll see the trailhead and some parking to your right before you get to the gate to the apartments. If you yearn for a really well-designed biking trail, it probably doesn't get better than this inside the city. The Oak Cliff Nature Preserve is 121 acres on an old Boy Scout camp. The Texas Land Conservancy has partnered with the Dallas Off-Road Bicycle Association to create a series of clearly marked, well-maintained bike trails at all levels of challenge, from beginner to semi-nutcase. And if you haven't seen this part of Dallas before, you're going to be knocked out by the topography ... maybe literally.