This 20th-century replica of a 13th-century castle has itself fallen into ruin.

This whimsical public art installation is a unique homage to Liverpool's industrial heritage.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

A public urinal so pretty, it was declared a national monument.

This small chapel is built of human bones and decorated with a golden skeleton.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

One of the shortest streets in York has an especially odd name.

A miniature Italianate fantasy village on the coast of Wales and the set of ITC classic "The Prisoner."

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

A haunting collection of the vanished and disappearing natural world.

This amazing example of Valencian Art Nouveau looks more like a cathedral than a public market.

Perhaps the most spectacular grotto along the Algarve coastline.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

A majestic lion statue guards this Parisian botanical garden, and feeds on an unsettling item.

Inside a former cabaret, seven floors of erotic art.

The final resting place of the "father of special effects."

A 400-year-old church covered floor to ceiling in ex-voto offerings from the faithful.

What looks like a normal building is really a hollow facade hiding a subway vent.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

In the best of all possible worlds, everyone will get a chance to see this statue in which Voltaire's heart is interred.

The first green space constructed on an elevated viaduct.

The history of radiation is on safe display at the foot of a radiation science laboratory.

A Belle Epoque bordello turned into a themed love hotel.