See four top-secret US spy aircraft of the Cold War era, including the legendary SR-71 Blackbird and the A-12 Oxcart.

Meant to resemble a massive tree, the building is the best example of Spanish organicist architecture in Madrid.

Explore an eerie, abandoned medieval citadel.

A former travertine mine traces the geological history of this unique desert filled with crystalline blue pools.

The mysterious "Candelabra of the Andes" could represent anything from a god's trident to a hallucinogenic plant.

An intricate network of underground tombs carved into volcanic rock.

Opened in 1956, the first modern indoor shopping mall in the world was inspired by the shopping arcades found in European cities.

Colin Stokes "got a bit carried away" and built a castle that looks like something out of Tolkien.

One of the last mosaic tile facades found in the city.

The famed architect designed this Minnesota gas station of the future with a lookout tower.

The oldest cemetery in Belgium.

This is one really big nut.

Hundreds of wooden coffins dangle from cliffs and caves in the Philippines.

This bronze cat looks out over the Linlithgow Canal.

True to its name, this bouncy walkway may be the world’s smallest suspension bridge.

The final resting place of a miniature monkey.

These gleaming gypsum sand dunes are the second-largest in North America.

A metal skywalk leads to the top of this striking granite outcrop in Porongurup National Park.

The hands on this clock appear to be created by two workers sweeping debris into careful positions.

A landscape decorated with enormous skull sculptures.

These unusual houses look like giant boats that washed ashore on a residential street.

Take a seat and hear a song by the composer Frédéric Chopin.

A submerged village appears when dam levels drop.

Whimsical wash tubs row down the stream as part of this Carnival celebration.