Looking for a mountain bike park in South County? Look no further than Black Diamond Open Space. This place has over 5 miles of trail. It also borders Henry's Ridge which has 14 miles of trail.
South of 4 Corners on Maple Valley Black Diamond Road to SE 276th and take a left (west). Follow along and it will turn into SE Maple Ridge Drive. At SE 281st Way just after the Skate Park and across from the water tower take a right and park along the road and go in at the "Boulders".
For the fitness challenge, park in the western parking lot off of highway 169. Head west towards the Mainline Trail and follow the signs.