This chimerical bridge/tunnel appears to dead end right into the sea.

A 19th-century subterranean reservoir repurposed as a contemporary art cave.

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

These medieval skyscrapers dominate the skyline of this small Tuscan town.

Overlooked amid the tourist bustle of Florence, this museum is dedicated to the craft of stone inlay.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

This strange bovine gargoyle is said to have been put in as a passive aggressive form of revenge.

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.

Pilgrimage site for star-crossed lovers.

Ancient burial grounds of the wealthy.

This Swedish astronomical clock was in storage for almost a century before its glorious workings were put on display once more.

It houses the remains of a 17th-century version of the Titanic.

Now a hotel, this former bank was the site of a robbery that spawned a psychological phenomenon.

An abstract monument to a symphonic composer.

A subterranean house of worship carved right out of the bedrock.

Hundreds of prehistoric stones, arranged in perfect lines in a French field.

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

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

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

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.