A library where thousands of books explain how to avoid another Great Recession.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

This allegedly haunted 16th-century tower house-turned-museum exhibits thousands of spectacular objects.

This series of Scottish caves has no clear purpose other than baffling historians.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

The fountain marks the area where hundreds of accused witches were burned at the stake.

One of the American Southwest's most extensive collections of Navajo rock art.

America's smallest national park site is the former residence of exiled Polish national hero Thaddeus Kosciuszko.

The oldest surviving presidential residence in the United States.

A forgotten "city of water" underneath the famous Trevi district.

This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

The mystic whose incorrupt corpse still attracts the faithful.

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

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

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

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

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

A stonemason's hilarious revenge came in the form of this peculiarly positioned gargoyle.

An old department store turned Nazi prison turned artist commune.

Inside this Jewish cemetery is a memorial to soldiers who deserted the German army and were executed.

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

Once a path for Jewish funeral processions, this unassuming alleyway is rich in local lore.

An eerie, derelict amusement park in Berlin.