Semi-precious Blue John stones have been mined in this cavern system for centuries.

Remnants of the 16th-century defensive wall still stand unassumingly within Edinburgh.

One of the largest underground systems runs under Canada's largest urban center.

One of the Seven Wonders of the Modern World holds the world's tallest metal staircase.

5,000 skulls in memorial to those killed by the Khmer Rouge.

A palace destined to never house a king.

An abandoned Cambodian resort that mirrored the downfall of the country as it was happening.

Don't be fooled by this fake medieval facade even if it is almost 300 years old.

This massive wooden building contains a giant Buddha, healing pillars, and tame deer wandering the grounds.

This giant bronze Buddha, the third largest in Japan, is the last in an ill-fated series of statues.

A bronze statue dating back as far as 1252, still has remnants of gold on its right cheek from ancient gilding.

The 10,000 Torii shrine.

Thousands of narrow alleyways in an ancient medieval city make up what's believed to be the world's largest car-free urban zone.

The world's northernmost aquarium looks like it has fallen over.

This functioning parish church is also the site of many concert performances due to its wonderful acoustics.

The tower was originally used as a chimney for the waste incinerator of St. John's Precinct and Market.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

The site of the famous Nazi book burning campaign of 1933 remembers its "Night of Shame".

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Yale University's home for rare works, including the mysterious Voynich Manuscript.

A moving memorial to the fallen and missing from WWI trenches.

All unmarked mute swans on the Thames are owned by the Queen per a tradition that began in the 12th century.