A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

The Gaudí-inspired building that was the start of Terrassenc modernism.

Two small chapels housed inside an ancient tree.

An awe-inspiring giant blue whale jaw bone stands in the center of this Dutch island.

Rich with fauna and flora, nature-lovers can walk across the sea at this UNESCO World Heritage spot.

Take a stroll through the hellish grotesques of Hieronymus Bosch in this elaborate Netherlands church.

Wonderland replication in progress by one persistent man.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

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.

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

An eerie collection of the surviving structures from a past celebration of the future.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

The world's largest wooden structure.

Giant eggs, walls of bread, and nightmare surreality mark the largest collection of works by Salvador Dalí.

A lush indoor jungle fills this bustling Madrid transportation hub.

This "social palace" housing complex created a relatively stable and self-contained worker's society... for a time.

Rows of multicolored bathing huts paint the sand dunes with pops of color.

A small house sits between two huge rocks, with its back to the sea.

An unusual sand beach in the middle of a forest.

This building’s ghostly exterior reflects its former lives as a prison, school, and funeral home.

This otherworldly French waterfall looks like its waters have turned to stone.

Miles of man-made caves and tunnels are currently used for cultivating mushrooms.