This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

A trading post in the North Pole where children send letters.

This frozen tunnel in central Alaska is both an engineering feat and a valuable climate classroom.

The ghostly remains of what was once the world's richest copper mine.

The king of U.S. high points towers over every other peak on the continent.

This whimsical stacked cabin looks like something out of a children's book.

The easternmost town in Alaska can only be accessed from Canada.

Iceland's "Smoky Valley" is a beautiful river that is shrouded in a constant cover of steam clouds.

An abandoned lighthouse awaits its destiny: being buried under shifting sand.

Plaques on its facade commemorate the Tiber's most destructive deluges.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

What was once England's second-richest abbey is now a haunting ruin.

Deliberately hidden for centuries, the magnificent Saadian Tombs were eventually uncovered in 1917.

A Moroccan getaway in the mountain range that plays the Himalayas' stunt double.

The remains of a magnificent medieval fortress that was the capital of a vast empire.

A statue erected in honor of the toadish nickname given to Jersey residents by the French.

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

An early 20th-century bullring converted into a modern shopping center.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

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.