Bradley Park, Wilton
Although Bradley is a somewhat small park, you can ride any section in both directions and string a bunch together for a solid hour or so of decent riding. Generally folks head in from Oak Ledge Lane. Take a left at the three-way intersection and continue around the park in a clockwise direction. There are a number of yellow-blazed offshoots as well. Eventually these will be joined to provide another loop.
Everything on the main trails is fairly easy but there are a few hills, roots and rocks, as well as a couple of rollers and drops scattered throughout the park. There are also a few wooden boardwalk/bridges. Not worth a long drive because of the size, but if you're local it's a lot of fun and fairly scenic.
For moreinformation see the Fairfield County NEMBA Website.
Good Morning Wilton article on Bradley Park.