Breathtaking and huge 430 year old maps of Italy.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

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

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Go inside to really appreciate this 500-year-old technological masterpiece.

A particularly disconcerting tribute to Irish martyrs.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

One of Ireland's most infamous prisons for rebels including men, women and children.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

A haunting collection of the vanished and disappearing natural world.

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

19th century pendulum and a clock restored by a rogue group of guerilla artists.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.

This bridge was constructed from the rubble of the infamous Bastille.

The celebrated eyesore created by starry-eyed sweethearts.

France's most famous cemetery, with some of its most curious tombs.

The mummified heart of Louis XVII, the lost dauphin of the French Revolution.

The famous winding walk at Chartres is surrounded in mystery and myth.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

Historic medieval fortified city in southwest France.

This French castle is said to have once held the Holy Grail but is now a gorgeous mountaintop ruin.