In the Black Hills of SD, they have the Mickelson Trail. It was once a train track that serviced all of the gold mines, hauling ore to the smelters. When abandoned, they tore up all of the tracks, but left the trestles that go over canyons. It is now open to hiking, horseback riding, and bicycles. It goes through some beautiful countryside.
I have hiked about 20 miles of it carrying a backpack with mining gear. I would park in the nearest lot and hike to a location that I wanted to scout. You meet some very nice people while hiking trails.