The colonial city's social history is reflected in its fanciful door knockers.

The world's greatest slide descends 18 stories from this looping mountaintop viewing platform.

A museum of alchemy and a basement laboratory all housed in an ancient building in a Gothic tower.

Thirty creepy ghosts now inhabit this decaying 14th-century church.

A Jenga-style cylindrical tower of books that appears to go on forever.

The hidden lair of an alchemist rediscovered in a 2002 flood.

A church of bones, decorated with 40,000 human skeletons.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

This cemetery overlooking the Benbulben rock formation is the final resting place of one of Ireland's most beloved poets.

This pub built its reputation pouring post-shift pints for employees of the cemetery with which it shares a wall.

This 14th century tower house was once the home of Irish poet W.B. Yeats.

The Grand Lodge of Ireland is one of the oldest in the world, full of fantastical, elaborately themed rooms.

Though they've since been renamed, these two streets hint at Dublin's darker days.

More than 5,000 artifacts donated by the people of the city, plus a room entirely devoted to the band U2.

The final resting place for the remains of 143 Habsburg royalty.

An allegedly haunted mansion with a tragic, tawdry past.

The historic bar where local ship captains, traders, and gold miners would come together to do business a century ago.

Make your reservation to have coffee with some kitties.

A huge musical sculpture and other art installations on the National Oceanic and Atmospheric Administration grounds.

Recovered from the brink of extinction, at home in the Financial District.

San Franciscans leave gifts and messages for the magical beings that live behind the tiny, mysterious door installed on a tree in Golden Gate Park.

A psychedelic labyrinth on the San Francisco bay.

A huge musical instrument played by the ocean.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.