This massive subterranean fissure is known as the "underground Grand Canyon."

This ominous Albanian fortress houses tanks and downed planes as a reminder of their victories over Western imperialism.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

These sacred Mesoamerican ruins feature peculiar petroglyphs hidden in the stones.

The place where World War I began.

A spectacular walk on the flank of a gorge.

Louise Bourgeois' 30-foot-tall steel spider sculpture.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

Stormy conditions send jets of seawater bursting through holes in the cliffs.

This Arab fortress was once the largest citadel in Western Europe.

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

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

One of Europe's oldest yew trees has lived more than 2,000 years.

Two large posteriors in one giant statue.