Trail Running in Seattle in Fitness Forum Posted May 29, 2006 Mercer Slough is pretty cool too. If you run around Mercer Slough, you're going to have to run in circles in order to even run 2 miles. I don't like running there. Robinswood park in Bellevue has a 4 mile trail out and back that is nice, soft dirt/pineneedle mix. You can also run down the sidewalk and loop around through the blueberry fields. If you want more info, just ask me. Cougar Mountain Trailhead off Coalcreek Pkwy in Bellevue/Renton also has tons of great runs. Not sure how long of a run you're looking for, but there are a lot of 4-10 mile loops. Just make sure to study the map at the trailhead first before starting. A lot of my friends have ended up running to Issaquah on accident.