Deep in the Guatemalan jungle stands an ancient pyramid that once marked the reign of a king.

A natural swimming hole that was once a ceremonial center for Mayan priests.

Sparkling, calcite-covered skeletons of children who may have been sacrificed to appease an angry god.

The largest greenhouse in the world is home to over one million types of plants.

Jumping-off point for a climb up Mt. Everest is the most dangerous airport in the world.

The highest monastery in the world operates a tiny guesthouse with doors open to all.

Last stop before the top of the highest peak in the world.

This is one of the last surviving structures of a once vast palace complex.

This historic square in Nepal is home to temples dating back to the third century.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

The largest bell in the world has been swinging high above a Cologne cathedral for almost a century.

This demon atop the Notre-Dame de Paris looks utterly bored.

One of the Seven Wonders of the Modern World holds the world's tallest metal staircase.

Housed in a 20th-century prison, this small museum recounts local Nicaraguan myths.

Climb atop one of the world's longest and heaviest trains for an unbelievable journey across the Sahara Desert.

Five ancient libraries, little changed for centuries, preserve a medieval archive of Quranic lore and civic documents

An architectural relic that survived the hands of time.

This remarkably well-preserved mosque stands amid an 11th-century caravansary.

A geological bull's-eye visible from outer space.

Destroyed numerous times, this centuries-old bridge has always been rebuilt with its original design.

In the heart of Tirana, this underground nuclear bunker has been transformed into a museum.

An Albanian monument to the Communism that nearly crushed the country is now a crumbling wreck.

A memorial to the atrocities of the People's Socialist Republic of Albania.

Once the fallout shelter of a dictator, this sprawling bunker is now a combined history museum and contemporary art gallery.