Mount Toby is kind of a hidden gem in Western MA as it has a great variety of terrain and trails which has become a favorite for many local trail runners. A description and trail map can be found here:

https://eco.umass.edu/facilities/our-forest-properties/mt-toby/

Beautiful circular trail, running on the borders of the Municipality of Schalksmuehle. The whole trail is well-marked with an S in a circle. Also it is a marked hiking route you will be on your own most of the time. Trail running through the beautiful nature of the "Sauerland" and is also crossing the Glörtalsperre which allows you to take a dip in between. If you decide to run self-supported, Glörtalsperre, Brenscheider Mühle and a gas station in Heedfeld are options to refill. Of course it is not the best circular trail in the world if you compare it to options you have e.g.