A luxurious doomsday bunker hidden beneath an unassuming Las Vegas home offers the best of subterranean suburbia.

An underwater statue of Christ blesses the depths off Key Largo.

Over 120,000 curious objects that have shaped our modern world.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

The only natural cave bath in all of Europe.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

This unassuming bookstore in the heart of Madrid is one of the oldest in Spain.

An exact replica of a colossal Olmec head sits atop a pyramid within a Madrid traffic circle.

Nicknamed the "Spirit of Paul Klee," this colorful apartment building features an array of multicolored panels.

Five million people are laid to rest here, more than the population of Madrid itself.

The morbid items in this small and hidden museum are not for the weak stomached.

Stuck in the middle of a modern Madrid city block are the remains of a 19th century sports complex.

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.

This funky former tobacco factory is one of the most striking examples of Madrid's cultural diversity.

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

The extravagance of Portugal’s "Pink Palace" resulted in a noble title being awarded to its owner.

This unassuming chapel in Portugal plays host to a ghoulish collection of bones.

Perhaps the most spectacular grotto along the Algarve coastline.

One artist's collection of homemade handicrafts doubles as a monument to 20th-century material culture.

A perfectly circular lake is formed by the crater of an ancient underwater volcano.

Bits of flat terrain surrounded by cliffs make one of the most beautiful landscapes in the Azores.

The hotel room where Janis Joplin tragically died has now become a makeshift shrine to the singer.

A quirky collection of figurines backdropped by city views is hidden next to a popular restaurant in the Hollywood hills.

This unique structure in suburban Austin is made up entirely of other people's castaways, and constantly changing.