I live just behind the woods and run it at least twice a week. If you stick to the outer loop it could be as long as about 3.5 miles. Good enough to keep me fit. Trails are well maintained, fallen trees are removed fairly in time. In my active hours which is late afternoon, normally there are not a lot of people, sometime I even feel I am alone.
I live in Stow and this is my favorite mountain biking trail. It's relatively flat and wide, but there are several single tracks throughout. I typically start on the Blue trail and explore. Gardner Hill is a pretty difficult climb and there are a few sections with some tight turns on the south side near the Assabet River. I've been there about a dozen times and I don't think I've seen all the connecting trails yet. This is a fun one to explore. I've seen some great wildlife out here as well. Snakes, foxes, owls and deer. I've also hiked this with my 2 older daughters and it was really enjoyable...pretty kid friendly, but bring bug spray in the summer.
I live nearby. Be cautioned that trail markers (like many in Mass) seem to be made for those who know their way, not those who don't. The skiing is wonderful with the right snow...but know where you're going before you head out. It's a great bike trail in the summer.. But dogs are NOT allowed on the trail. It's an Audubon sanctuary, and they try to keep it safe for the migrating wildlife (versus dogs).
Great spot if you are in the Stow area and want to get outside without having to travel. The trail system is well maintained and the main trails are well marked. Side trails dead end to marked private property but off a way to extend your day. some os the ones off the blue trail look like favorites os mountain bikers.
I went on a sunny, warm Sunday from late morning until early afternoon and it wasn't crowded. Most walkers did have dogs, some leashed and some not. This is a good place for running as the footing is generally pretty good and there are some places for hill sprints. As the previous poster said, the main trails are wide and level, which is good for children and those who prefer a walk to a hike. The trail along the river is especially nice, and this network would be very enjoyable when the leaves have turned a little later in the fall. I plan to try cross country skiing here and will post this winter. For trail maps see the link and look under Gardner Hill. Have fun :)