Thrilla is popular urban mountain biking loop that connects the Tolt Pipeline trail to the Puget Sound Energy Powerline Trail, also known as the Redmond Powerline trail, through small sections of Trilogy trails, the Redmond Watershed Preserve, and the Sammamish River trail making an 18.33 mile loop.
One can park at the baseball fields off NE 145th street and start the loop there on the Sammamish River Trail (SRT) and run north to the entrance of the Tolt Pipeline Trail and the famous Heart Attack Hill climb. Follow the Tolt Pipeline trail up and down steep punchy climbs for about 11 miles until the turn off for the Collin Creek Trail on the left. The Collin Creek Trail is a part of the Trilogy trail system and will take you right into the Redmond Watershed Preserve and will eventually turn into Siler's Mill Trail at a wooden zig zag gate. Follow Siler's Mill Trail until it intersects into the Redmond Watershed Trail (RWT) at another wooden zig zag gate. Turn left onto the RWT until it ends at the Puget Sound Energy Powerline trail (PSE trail) Also known as the Redmond Powerline trail. The PSE/Powerline trail heads west out of the Redmond Watershed Preserve and quickly gets diverted onto the road. Do not worry this path is often taken by trail users to get back to the PSE along the north side of Farrel McWhirter Park. Go Left on 206th Ave NE and then right on 116th, then left onto 196th Ave NE. You will see signs for both the park as well as the PSE/Powerline trail. The PSE/Powerline trail skirts the north side of the park and quickly pops out at the crossing for Avondale Road. Now you can follow the PSE/Powerline trail all the way down to the Sammamish River Trail (SRT). It's about 3 miles on the SRT back to complete the loop.
Thrilla is a beautiful route that connects some major urban trail systems together for a really fun loop. Running mostly on a wide gravel trail there are challenging climbs with views of the mountains on a clear day. There are sections of super fun single track deep in the woods but still close to civilization, and even sections of pavement on quiet streets and paved trails. You really get the best of all surfaces while going between busy trails and solitude. This is a classic MTB/gravel biking route that can be enjoyed by runners as well.