New York stories of mutants living underground go way back, and if you believe them, well...enjoy. The Freedom Tunnel is the one place in the city you can visit that was home to actual urban cave-dwellers—hundreds of them. Check out the documentary Dark Days by Marc Singer. The squatters were mostly homeless looking for safety and privacy, but some seemed positively drawn to eternal dark. They were forced out when AmTrak reactivated the tunnel, but who knows what’s down there at any one time. It’s a good place for explorers who like their trespassing tinged with dread.