This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

These hut foundations are believed to be the residence of Romulus, founder of Rome.

This large, circular tomb is the final resting place of the first emperor of Rome.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

Hidden within this iconic mountain are a set of World War II bunkers once used by German forces.

Architectureal fantasy quarter of Rome.

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

A neo-Gothic mansion now houses a wunderkammer of analog tech that hits on all the senses.

Dine amidst exotic plants at this former royal greenhouse.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

The townhouse where the "Blood Countess" Elizabeth Báthory started her murderous career.

Weird wax anatomical models reside here, as do other anatomical specimens.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

The video game-themed street art first popped up in the French city.

With a history of slaughter, feast, and famine, remnants of the pork industry decorate this area--even its church.

This museum in a Paris apartment gives a unique look at the iconic French singer's life.

Skeletons, medical artifacts, and other obscure and precious treasures all displayed in a wooden pharmacist's cabinet.

Two awe-inspiring globes from the reign of the Sun King hang from the ceiling of France's national library.

The former home of France's controversial pop maestro is almost completely covered in ever-changing tributes and graffiti.

A unrivaled and rather horrifying collection of wax dermatological models.

Paris' fabled purveyor of exotic taxidermy and natural history curios.