The Middlesex Fells Reservation is a vast expanse of woodlands, hills, and rocky outcrops, with the reservoir itself being its centerpiece. There are paths all over the area, with the Rock Circuit Trail being one of the best and most logical running routes. The run takes you to the reservoir itself, as well as some cool little outcrops like Pinnacle Rock and Boojum Rock. There's also the option to detour to several other outcrops and Cairn Hill for those who find this loop too short.

Along the route you can expect to see an array of trees and flowers, as well deer and maybe even some foxes or coyotes. There are also numerous species of birds living in the area, so the twitchers out there will enjoy this run.