One of Antoni Gaudí’s earliest buildings, built between 1886 and 1890 for the industrialist Eusebi Güell.

Ancient snack bar of the Roman Empire re-opened.

The walls and streets of the ancient city are peppered with penises.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The glowing blue Nymphaeum of Emperor Tiberius.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

The oldest volcanology research center in the world.

The once forbidden "secret cabinet" of erotic art from excavations of Pompeii and Herculaneum.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

Where Venice's gondolas go for a tune-up.

An extensive collection of reliquaries containing the bones of saints housed in the largest Catholic church in Venice.

Go inside to really appreciate this 500-year-old technological masterpiece.

Two stone columns flank the grand Venice square, but there were supposed to be three.

The only museum with its curator—and her pets—buried inside.

Those who own or stay at this 500-year-old, allegedly cursed house often meet terrible fates.

Baroque celebration of the end of the Great Plague of Vienna.

Launched by Napoleon's soldiers more than 200 years ago, a cannonball remains embedded in the tower wall.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

The massive white mound and accompanying water terraces are a striking geological oddity.

These 13th century documents come housed in 18th century shelves organized by a 19th century historian.

An underground city of salt.