Hidden beneath the streets of London is a secret subway that only carried mail.

Gothic tower where Lord Alfred Tennyson wrote the poem "The Sleeping Beauty."

A monolithic monument in Greater London.

Putting the "mod" in "modular" since 2000.

Shakespeare, David Bowie, Dr. Who, the Saxons, Druids and Romans are all claimed to have all made their mark on these massive man made tunnels.

This tunnel entrance is built to resemble a grand castle but no one is quite sure why.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

These azure waters were thought to lead to the Mayan Underworld.

A sprawling Baroque park with 300-year-old hydro-pneumatic waterworks.

Trick water gardens from 1619 featuring a 200 piece mechanical theater powered by water.

Massive puppet-automaton machines created by French artist collective Machines de l’Ile.

The Origin of On the Origin of Species.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

An otherworldly restaurant perched on the edge of a jagged cliff next to a medieval holy city.

A cave covered with bizarre stalactites of cloth.

A mecca for India's Jains.

This smaller cousin of the Forbidden City has gone from ancestral sacrifice to tourist's whispers.

Eighty million natural history specimens call this gargantuan museum home.

High-end antique collection housed in a centuries-old church.

Landbridge created by the South Korean version of Moses.

Asia's largest limestone cave is home to a world of plastic goblins and gold mining history.

An Ethiopian "Jerusalem" featuring a church hewn out of a single rock.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

Gods clash with machines in a power plant regenerated as a museum.