I revisited Estabrook Woods recently and a few more unpaved trails around Carlisle, MA. I was hoping to find a new way across Carlisle, south to Concord, but unfortunately, it seems that nearly all trails through Estabrook forest are more suitable for mountain bikes or even fat bikes, and not bikes like my Poprad. Many of these paths are walkable but can't be easily traversed by bike. They are too narrow, too overgrown, too rocky and too bumpy in places. The only one that is definitely accessible is the trail connecting both paved ends of Estabrook Rd, on the western side of the forest (see the map below). But even there I wouldn't approach it without at least 35mm-wide tires.
Estabrook Woods Trail in Carlisle, MA.
I added some comments on the map below so you can decide for yourself, which way to go, should you be in this area.