Rome's semi-secret peephole vista is also a former Crusader stronghold.

An alchemist's "magic door" stands in the middle of a Roman park.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

This curious building hides eclectic details like medieval gargoyles alongside naked angels and Art Nouveau mosaics.

Architectureal fantasy quarter of Rome.

A medieval setting reimagined into a unique art alley.

The most confusing clock in New York.

New York City's only radical feminist independent bookstore.

More than 250 sakes are available in an izakaya hidden in the basement of a Midtown office building.

This subterranean oyster house has been the pearl of Grand Central Station since 1913.

This abandoned seaside fortress is now simply an imposing ruin being taken back by nature.

This plot of old-growth forest is the largest surviving remnant of New York City's original woodland.

Unrepaired walls from a 1920 anarchist bomb attack.

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

This futuristic airport terminal was abandoned for decades before reopening as a hotel—with a vintage plane of its own parked out back.

A hyper-luxurious, 12,000- square foot home might be buried beneath Queens, still waiting to protect you from nuclear missiles.

A WWI fighter plane and turn-of-the-century penny candy shop are among the unexpected features of this Financial District building.

A Manhattan courthouse hides a small but scathing memorial to Holocaust injustice.

Slyly buy a shake in the Parker Meridien lobby.

This abandoned subway station can still be seen on regular commuter trips.

This ruined fort hidden at the top of Central Park can't seem to keep from losing its historical plaques.

Tucked away amidst some of the most famous addresses in the world is New York's only fraction of a street.

This former Norwegian sailor's church is slowly being taken over by ramshackle robot musicians.

Nondescript elevator doors open to reveal a stunning, surreal world.