This unreal Portuguese palace looks as though it's made from a pile of different castles.

This star-shaped military outpost is now simply trying to protect itself from neglect.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

This monument to a veteran of the Mexican-American War is one of only two in Manhattan that serve as an actual mausoleum.

A whimsical, but often overlooked clock in Park Avenue.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

Commemorating the spot where the famous scientist fed his pigeons.

Cheap pizza and all of your naughty bedroom needs housed in a stunning example of Art Nouveau architecture.

The New York hotel where tragic visionary Nikola Tesla spent his final hours, destitute and alone but for the pigeons.

There are owls with glowing eyes in Herald Square.

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

A bit of retro transportation flair preserved in the world's largest department store.

"X" marks the spot of an echo chamber in the middle of a plaza.

Secret refuge and museum of the Duke of Florence.

The famous sculptor left his mark on this Italian wall in an internationally protected example of street art.

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

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

Italy's "New Mountain" rose from the ground in a volcanic eruption in 1538.

Windblown rock formations in an ancient Roman quarry.

Mountain where Jesus was first tempted by the Devil.

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

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

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