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

A restaurant and observation deck built in a unique broadcasting antenna.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The most visited, and possibly most controversial, museum in Germany.

A towering monument in Spain has proven to be more labor-intensive than initially planned.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

A lush indoor jungle fills this bustling Madrid transportation hub.

An ancient Egyptian temple in the middle of Madrid, Spain.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Hear the quietest sound from across the dome.

This 14th-century temple is also known as the "Temple of the Golden Pavilion" for its gorgeous gilded reliquary hall.

A beautiful bamboo trail tucked in this famous Japanese shrine.

The sound of swaying stalks in this stunning grove has been named a governmentally recognized sound.

Every Sunday, Bogotá turns 75 miles of its city streets into a bicycle superhighway.

Pilgrims each carried a brick to the top of Mount Monserrate to help build this historic sanctuary in Colombia.

A celebration of Colombia’s premier contemporary artist.

This Bogotá museum houses the world's largest collection of pre-Columbian gold relics.

Located outside Medellín, this Colombian park focuses on conservation and sustainability.