This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

An early 20th-century bullring converted into a modern shopping center.

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

Houses are tucked between, on, and underneath giant boulders.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

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

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

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

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

This curious, round temple is the oldest still-standing marble building in Rome.

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.

The oldest operating pharmacy in the world features 800-year-old recipes.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

The yawning maw of this pagan visage is said to bite off the hands of liars.