This amazing example of Valencian Art Nouveau looks more like a cathedral than a public market.

A fortress off the West coast of Portugal that dates back to 1502.

Sound travels strangely in this underground whispering gallery.

Dublin's most modern, visually spectacular bridge is modeled after Ireland's national emblem.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

This tri-part waterfall is a little bit of fairytale beauty in the heart of Luxembourg's Little Switzerland.

The verdant mossy ruins of a Franciscan monastery lie in the remote Sintra hills awaiting exploration.

"Stairs of the Turks", a chalky white cliff eroded conveniently into stairs, allowing for easy pillaging.

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

A mysterious ancient elephant said to possess magic powers is now the symbol of a Sicilian city.

142 ceramic steps become a mosaic once a year.

Italian cave with exceptional acoustics and an unsavory history.

A historic Christian shrine nestled within a spectacular natural cave.

A 12th century church completely covered in shells.

At night, bats patrol this magnificent 18th-century space in search of book-eating pests.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

A man has revenged his true love's betrayal through tears and stone genitalia.

It houses the remains of a 17th-century version of the Titanic.

Stockholm's deepest subway station is also a stunning ecological wonder.

Ruins battered by centuries of war and disaster offer a wondrous glimpse of medieval Ireland.

The mummified heart of a saint lives on in this church—after a brief hiatus when it was stolen.

An ancient neolithic tomb that only sees the sun twice a year.