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

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

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

The oldest giants in Catalonia are now displayed in a 14th-century Gothic church.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

A beautiful but toxic fountain of mercury.

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.

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

A series of abstract, silly sculptures represent the works of a great modern classical composer.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A mechanized clock where a man fights off a dragon, crab, and rooster.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

The oldest stone house in Paris was built by its most famous alchemist.