This man-made mound monument was built out of soil from all across the Polish empire.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

These aggressively sustainable art homes look like something out of 1970's science fiction.

A floating cat sanctuary on an Amsterdam canal.

Walk through Czech history in Prague's largest graveyard.

Descend 2,030 years into the past in an ancient tunnel built to support Jerusalem's most famous wall.

This historical Netherlands fortress still bears the marks of its single siege.

This beautifully designed star-shaped fort was the premier defense system of the late 1500s.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

This house's itty bitty size means no humans allowed.

The splendor of this 17th century golden chapel has led it to be called the "eighth wonder of the world."

Europe's largest natural bridge has a 19th century royal chateau built into its side.

This ancient Irish tower could easily have stood in for Rapunzel's prison.

A 500-year-old series of tunnels long believed to be folkloric was uncovered beneath the streets of Puebla.

An Aztec temple, the largest man-made pyramid in the world, sits buried in earth with a Spanish church set on top.

Where the Great Wall of China meets the sea.

The tunnel's elegant proportions keep you snug with no claustrophobia freak-out.

Sacked by Vikings, blessed by William the Conqueror, dealt a fatal blow during the French Revolution—these ruins have seen it all.

These steeply terraced ruins are a stop along the Inca Trail to Machu Picchu.

A fairytale Gothic castle steeped in Nazi treasure conspiracy theories.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

The whimsical twist of this spire was either caused by the Devil, an unexpected virgin, or lead.

These towering spires and glowing walls are carefully crafted from hundreds of thousands of icicles.