Cave of the Apocalypse
Patmos, Greek Islands, Greece[2.3 miles]
This creepy cavern is where St. John the Evangelist had his apocalyptic revelations (which became the last book of the New Testament). Adorned with 12th-century wall paintings and shimmering icons, the sacred grotto is often packed with Greek pilgrims, as well as day trippers from the many cruise ships that service Patmos.
Best for ages: 18+ | Free