Great place for a mid/long distance run, or even a short one. Starting from Darnestown Rd all the way to Rockville Pike it's about 5 miles long. So, while training, I've even done 20 miles on this path, doing twice the mentioned route and back. There are some hills, but not too many nor too elevated. And what's best - and rare in this neighborhood - you only have one hard-to-cross traffic light along the way (Falls Rd).