Lackawanna State Park is a 5.5 mile loop trail located near Shunk, PA. The trail is primarily used for hiking and is accessible from April until October.
Lackawanna state park has a bunch of trails that loop in and out of each other -- you essentially can go as far or as short as you want. It was about 8 miles to go around the whole lake. Not the best scenery (you only catch glimpses of the lake), but the trails are well-maintained and well-marked. There are free maps (as well are posted ones) at most trailheads which is nice. There's also boat rentals which was fun. I would recommend.