The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

A magical museum of fairy tale treasures near Cyprus' buffer zone.

The ruins of a fairytale castle with a tumultuous history stand high atop the mountains.

A former imperial sea-fortress and Soviet prison.

This medieval Estonian tower provides access to a series of tunnels that have been home to soldiers, punks, and fine art.

A secluded art gallery hidden within the cellars beneath Tallinn’s medieval monastery.

A cylinder monument with a spectacular vista commemorates a friendship that some say never existed.

Luxury hotel turned into a refugee camp, then turned back into a luxury hotel.

This architecturally eclectic fortress witnessed centuries of bloody turmoil, including the massacre of its ruling clan.

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

The European towns of Brașov and Râșnov each have proud signs reminiscent of the Hollywood sign.

This snug medieval lane is one of the narrowest streets in the world.

This Transylvanian church has changed its denomination four times.

The Natural History Museum that time forgot.

Some call this eerie forest of crooked trees the "Bermuda Triangle of Romania."

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

Known as the Hintz House, this medieval pharmacy has been an apothecary's haven for nearly 450 years.

Ancient rock-hewn town that witnessed key events of Georgian history.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

Indents in the pavement are all that remain from a grisly death machine in Paris.