Tunnel Mountain Trail is a 22.6 mile loop trail located near Woodward, Pennsylvania. The trail is rated as difficult and primarily used for mountain biking.
attempted to hike through the tunnel with my dog. The tunnel is closed due to deteriorating conditions and the "temporary trail" that has been blazed as part of the MST is rated a lot higher.
If this is the one I'm thinking of. Many fond memories of this old decrepit tunnel. Truly frightening at night. Never ventured far from tunnel tho I hear it's a beautiful walk.