Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

Next to the Leaning Tower of Pisa is a cemetery home to ancient sarcophagi and disturbing murals.

A man's head is enshrined beneath a statue near the first building constructed for the modern Olympic Games.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

This mystical orb covered in strange symbols is thought to have been used in ancient Greek magical rituals.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

Legend says this sacred tree was a gift from goddess Athena.

These caves secretly held national treasures during World War II.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.

This legendary city has been a tourist attraction for centuries.

This 15th-century island fortress later served as home to the executioners no one wanted to live near.

The hallucinogenic center of the ancient world.

This ancient Egyptian obelisk still bears the wounds of World War I.

A 1950s beatnik coffee house, turned 60s counterculture hotspot, turned modern music venue.

A unique tribute to the millions of animals who served and died for the British military.

The fierce beast perches atop a pedestal marking where the historic City of London gates once stood.

These mysterious Viking chess pieces spent centuries hidden on a remote Scottish island.

A naturally mummified 2,000-year-old man.

London's smallest police station is barely the size of a phone booth.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

The television series' iconic giant foot was borrowed from this classical painting.

A statue of the legendary Celtic warrior queen who fought the Roman invaders stands in one of the cities she once destroyed.

Giant, friendly pelicans in Central London, the most unlikely of places.