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

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

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

Opulence and fantasy collide in this royal chair which is supposedly made with unicorn horns.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

A museum filled with tiny, adorable versions of the mighty Royal Danish Navy.

Old Danish castle immortalized in Shakespeare's Hamlet.

The largest bottled beer collection in the world holds over 22,000 unique beer bottles.

Beneath Denmark's Højbro bridge, a bronze merman and his seven sons forever mourn for the mother and wife who left them for land.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

A Parisian exterminator's shop whose storefront displays stuffed rats hanging from traps.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

A 30-acre garden inspired by the principles of modern physics.

A nuclear bunker built to shelter the politicians and important people of Scotland in case of nuclear attack.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

A book bound in the skin of an infamous criminal, along with countless other specimens.

Tiny effigies of the victims of Edinburgh's famous Anatomy Murders.

Shiny Brutalist box commemorates a pioneer of electricity and houses a railway transformer.

Rebuilt remains of a temple to Roman god Mithras.

A toy store with a century-long history preserves the craftsmanship of playthings of the past.

Louise Bourgeois' 30-foot-tall steel spider sculpture.