Lynn Woods in Lynn, Massachusetts is a beautiful place to hike, and you'll feel extremely lucky if you stumble upon open doors to both the stone tower on Burrell Hill, and the perfectly creepy pitch-black cavern of Dungeon Rock.
You can read the strange history of Dungeon Rock here. Dungeon Rock & the stone tower are generally open May 1 through November. There are complimentary trail maps at the parking lot. Stop at Bent Water Brewing, also in Lynn, after your hike.