Behind medieval walls in a corner of bustling Palermo is a breathtaking former mosque once inhabited by a wolf-taming hermit.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

A drawbridge named for a potentially intersex Polish national who fought alongside George Washington during the American Revolution, and an example of "Pulaski Red".

The one-time epicenter of American songwriting is now a little remembered Manhattan commercial block.

A grand New York post office that is home to mailman Santas, scraps of postal history, and a pneumatic mail system.

The most confusing clock in New York.

The notorious headquarters of a corrupt political machine.

An artist's cute bronze subway sculptures belie his violent artistic past.

Visit the monolithic tomb of America's most famous general.

The New York hotel where tragic visionary Nikola Tesla spent his final hours, destitute and alone but for the pigeons.

Curious crustaceans support an obelisk from ancient Egypt that now stands in modern-day Central Park.

Wine bottle sculpture with a ship's stateroom inside.

The name of this famed hospital was once a byword for the horrors of medical and psychiatric care.

One of only two commuter aerial tramways in the United States.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

Elevated freight railway turned wildly successful urban park.

Naturally formed rock city in Poland.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.