This once-forgotten oasis in the middle of Lisbon was first created over a century ago quite by accident.

The world's largest wooden structure.

Budapest's Communist-era statues, banished to the suburbs.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

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.

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

This unattributed sculpture in Amsterdam is hiding in plain sight.

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

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

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

A cluttered and astounding collection of antiquities and curiosities.

The anatomical-pathological collection of a man who changed surgery.

An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

Hidden on the 7th floor of a historic building, this Cajun spot features wall-to-wall bottles of hot sauce.

The gilded, masterful astronomical clock will calculate time, dates, and planetary positions for thousands of years to come.

This sublime architectural marvel is a rare example of an expressionist church.