Hiding the longest subterranean river known in the world.

This collection of over 50 murals celebrates Brussels' rich history as the self-proclaimed home of the "comic strip."

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

Climb inside an iron crystal magnified 165 billion times its normal size.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

Giant WWII fortresses that fired 8,000 rounds a minute, now home to thousands of pigeons.

A spherical "micro-nation" in the heart of Vienna.

Amsterdam's Red Light District leaves little to the imagination.

Amsterdam's narrowest house facade is a monument to 17th-century tax evasion.

Sail in for a ’dam good slice.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

This pirate-broadcasting-tower-turned-restaurant played a rebellious role in the history of Dutch television.

This bird-loving brewery is situated in an old municipal bathhouse, nestled beside a 300-year-old windmill.

One of Amsterdam's narrowest houses is located right across the canal from its widest.

Amsterdam's former hotspot for public executions and dissections.

An overgrown and largely forgotten cemetery lies hidden within the outskirts of Amsterdam.

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

A Portuguese Jewish cemetery filled with stunning grave monuments that date back to 1614.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

This unattributed sculpture in Amsterdam is hiding in plain sight.

The house that took a plunge into the facade of a museum.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.