Catacombs turned marketplace.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

A vast overgrown cemetery, once known as one of London's "Magnificent Seven."

The curios of pharmacist and collector Henry Wellcome.

An unusual round church in London with a Templar past.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

An alien church provides much needed silence in the midst of a Finland shopping center.

A subterranean house of worship carved right out of the bedrock.

Exploring the wilder, more passionate sibling of Erg Chebbi feels like discovering a secret sun-kissed planet from another galaxy.

A mud brick kasbah with a history of lavishness and traitorship.

An abandoned horror film set sits eerily along a highway through Hollywood's "door to the desert."

God's Saharan sandbox of wrath.

A fortified city, home to a remaining population of five families

Mosaics, storks, and brothels—this ancient city has it all.

World's largest film studio, where visitors tour the decaying sets that litter the harsh desert environment.

One of the most spectacular canyons in the world.

The "Little Ones," show Portugal in full miniature splendor.

At night, bats patrol this magnificent 18th-century space in search of book-eating pests.

Elaborate tile work in this railway station tells the story of Portugal.

A majestic hotel for dreamers rises from the center of a fairytale wood.

One of the largest Roman settlements in Portugal.

An abandoned mine now resembles a post-apocalyptic landscape of derelict buildings and blood-red pools of water.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.