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

A fairy tale castle in modern Rome.

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

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

The "Greatest 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.

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

This once-derelict building is now one of the most beautiful bookstores in the world.

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."

This elaborately decorated, fairytale-like Romanian royal palace is one of the most striking castles in Europe.

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

The real-life site of Ichabod Crane's infamous gourd attack.

Reforestation in action is the main attraction in this abandoned quarry.

A ruined mansion hidden in the woods of the Hudson Valley, home of a tragically doomed romance.