The ruins of an ancient Roman tomb hidden in the basement of a trendy clothing store.

These caves secretly held national treasures during World War II.

According to legend, this ancient column contains healing properties.

Legend says this sacred tree was a gift from goddess Athena.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

A former military hospital is now used to study and preserve artifacts of the Acropolis.

An ancient Greek monument and a Byzantine church coexist inside this cave.

Underneath one of the region's most historic roads lies the home of Plato's successor.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

An ancient site that has revealed incredible artifacts including portions of the Themistoclean Wall.

The medieval center of the Islamic world was also once the seat of Saladin's sultanate.

The massive cave church of Cairo's Zabbaleen community is one of the largest Christian churches in the Middle East.

Slum Settlement Filled With Mountains of Garbage.

This ancient structure is widely thought to be the oldest intact pyramid in the world.

Along the pavement of this neighborhood in Madrid are quotes from famous authors.

A statue commemorating a beloved stray dog who was adopted by the entire neighborhood where he lived.

A pair of gigantic baby heads greet passengers at Atocha Station.

A lush indoor jungle fills this bustling Madrid transportation hub.

Commonly acknowledged as the only public monument to the Devil himself.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

The remains of this misplaced church were moved here stone by stone.

Once a resting spot for King Fernando VII.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

This piece of early engineering is rather unknown despite its location in the heart of Madrid.