A home for Spain's version of the Tooth Fairy, hidden in an old gas company register.

Legend has it that the water from this fountain has miraculous healing properties.

A mid-14th-century tower that served as a prison for Spanish nobles.

A subterranean relic of the Spanish Civil War hides below this picturesque park.

A giant hand emerging from the ground beckons visitors into a park in Madrid.

Madrid's last horchata kiosk is a blue-and-white beacon of refreshment.

This girder was hit by a bomb during the Spanish Civil War, but nobody knew about it until 2016.

Built to celebrate the glory of a new queen, this forgotten monument has moved around Madrid three times, reflecting 200 years of political whims and city redevelopment.

The smaller of the three towers of San Marino is a former prison inaccessible from the ground level.

The world's most active stratovolcano is almost always erupting.

This 17th-century passageway is home to numerous bookshops, a witch legend, and the oldest pizzeria in the world.

This monastery built into a cliff hides a perfectly preserved hermit in a glass coffin.

This no man's land slicing through the island is strewn with abandoned relics of another time.

1513 Turkish world map, full of European state secrets and snarky commentary.

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

Legend says if you stick your thumb in the hole and it gets wet, your wish will be granted.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

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

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

The "Great Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

An ancient Roman temple first dedicated to an emperor's wife is now a church.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.