If there’s a highway to hell, there’s probably a gate to hell—well, there is. It’s located in what was the ancient Greco-Roman city of Hierapolis, which is now in modern-day Turkey.

Called Plutonium after Pluto, the gate was thought to be an opening to the underworld. It was first described by the ancient Greek geographer Strabo and Roman author Plinius. When Strabo visited, he described a thick vapor that would overtake the gate. During religious ceremonies, the castrated priests who ent