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

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

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

An alchemist's "magic door" stands in the middle of a Roman park.

Museum dedicated to literary greats of the Romantic Period is also the home in which Keats met his untimely end.

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

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

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.

This semi-secret storybook hedge maze is also the oldest garden in the city.

Mountain where Jesus was first tempted by the Devil.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Turntable anonymously received orphans, alms, and groceries.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

This knobby, drooping New Orleans oak is a favorite place both for climbing and for meeting giraffes.

A house of courtship where the Jazz Age's most storied lovers got their start.

This historic "City of the Dead" lies prominently in the center of New Orleans' famous Garden District.

This relatively recently abandoned brewery is a tragic reminder of the continuing effects of Hurricane Katrina.

A pink cottage covered in hearts served as a haven and a resting place for LGBTQ activists.

A little piece of Paris in the sultry south of the U.S.

Made of giant chains and hung with shackles, this iron cross honors those unknowns who perished under American slavery.

Introducing the Green Fairy to her fawning masses.

A museum and shop on Bourbon Street located in the former home of the second Voodoo Queen of New Orleans.

The restaurant keeps a hidden séance room on the second floor and reserves a table for the spirit of the former owner each night.