The Hermit's Castle Trail is a difficult 4.5-mile out-and-back hike in Erving, Massachusetts that leads up to a small cave in the side of a massive rock ledge.
The trailhead is located in the front yard of a residence on Cross Street and follows Briggs Brook to the top of the ridge. Follow the white-dot blazes (M & M trail Section 16) to the Hermit's Castle trail (blue-dot blazes). Here you have the option to continue on the white-dot to Hermit's Overlook and then circle down to the "Castle" itself where you reconnect to the white-dot.
The trail is very steep and crosses the brook several times for the first part of the trip. Descending to the castle is also very steep. The white-dot trail also provides access to the Farley Ledges Trail (red-dot) early on.