This 11th-century castle sits so low you can't see it behind the surrounding buildings.

The works of poetry's biggest names grace the walls of the city of Leiden, all carefully painted by hand.

An ancient Egyptian temple sits within a modern European museum.

A 'living museum' in Leiden, the oldest of its kind in the Netherlands.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

Amsterdam's former hotspot for public executions and dissections.

The attic of a four-century-old canal house hides a clandestine church.

Also known as the Blue Church, the building was consecrated to the daughter of Andrew II.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

Launched by Napoleon's soldiers more than 200 years ago, a cannonball remains embedded in the tower wall.

A sculpture of the beloved author surrounded by characters from his fairy tales.

Dedicated to a synagogue that was destroyed after having survived World War II.

View the ancient remains of buildings and the ancient "River of Hades" before hopping on a train.

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

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

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

An ancient octagonal weather station named for the eight Greek gods of wind.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

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

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

Monasteries on rock pillars, once accessible only by frayed ropes.

Believed to be the only Orthodox church in the world that features a free-standing pulpit.

The hallucinogenic center of the ancient world.