Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

For decades, Puerta del Sol has been illuminated by a giant, guitar-wielding bottle of sherry.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

The mummified right fist of a 1,000-year-old saint-king sits inside an ornate golden reliquary.

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

A series of caves under Castle Hill that once held the prisoner Vlad Tepes, better known as Count Dracula.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

Stone memorial that's said to predict the death of the pope and the site of the Cadaver Synod.

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

The "Great Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

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

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

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.

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

Architectural monsters are devouring this palace's every door and window.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

This bridge was constructed from the rubble of the infamous Bastille.

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

Site of a classic 19th-century physics experiment to prove the earth is rotating.

This modest marker near Notre Dame identifies the very center of Paris.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

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