Directions from Seattle Running Club Website:
The registration and start will be at the Sky Country Trailheadoff of 166th Way SE (NOT at the Red Town trailhead).
From I-90 Eastbound, take the Lakemont Boulevard SE (Exit 13) exit. Head south (turn right) for 2+ miles on Lakemont Boulevard SE. Turn left onto SE Cougar Mountain Way; go 0.6 miles and then turn right onto 166th Way SE. Follow this road through the gate and look for the parking lot on your right.
From I-405, take Exit 10 and follow Coal Creek Parkway east for 2.4 miles to the shopping center. Turn left at the light onto SE 72nd Place. At the stop sign, turn left onto Newcastle Road, which turns into Lakemont Boulevard SE. Continue on Lakemont past the Red Town trailhead until you reach SE Cougar Mountain Way. Turn right, go 0.6 miles, and then turn right onto 166th Way SE. Follow this road through the gate and look for the parking lot on your right.
For more information: http://seattlerunningclub.org/Events/Cougar/cougarmtn1.html