Longest road tunnel in the world features an air treatment plant and the illusion of daylight.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

The largest hewn stone in history.

The stones of this Incan wall complex fit together so well you couldn't fit a piece of paper between some of them.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

This was once the center of the Birdman cult, and is now a World Heritage Site.

The hallucinogenic center of the ancient world.

This legendary city has been a tourist attraction for centuries.

A devastated ruin in the south of Belize where British explorers claimed to unearth the Mitchell-Hedges Crystal Skull.

A fascinating insight into daily life in the Eastern Bloc.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

This stoic bronze soldier stands as a symbol of Russian sacrifice or Soviet oppression, or maybe both.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

A symbolic graveyard for the villages that perished during the Nazi invasion of Belarus.

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

A former Latvian headquarters of the brutal KGB secret police is now open as a grim reminder of their atrocities.

Flamboyant architecture from the turn of 20th century.

3,000 market stands in five former Zeppelin hangars.

A black cat protests the City Guild in Riga's Old Town.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

An architect's childhood fantasy treehouse made real.

A beautiful geyser under environmental threat.