The beautiful tunnel that ran from the lobby to Penn Station is still hidden underneath 34th Street.

The name of this tiny pocket park tucked between two buildings on Manhattan's Upper West Side is Latin for its location: "seventy-one."

Rat sculptures try to infiltrate the Graybar Building in an architectural tribute to New York City's nautical history.

The world’s oldest and biggest bookstore stocking only mystery, crime fiction, espionage, and thrillers.

A forgotten relic from New York's bygone trolley system hides in plain sight under a bridge.

The fanciest public restroom in New York City boasts fresh flowers, art, and a classical music soundtrack.

This lavish room at NYC's French Embassy is a rare relic from the end of the Gilded Age.

One of the only single-person private gravesites in New York City.

A quick trip around the globe through an amazing miniature exhibit.

This Russian bar-restaurant lies within a three-story underground bathhouse.

Underneath the bustling city streets, a hydroponic farm grows unique herbs in an urban oasis.

A Japanese temple, old German townhouses, and public chess tables offer a peaceful escape from the bustle of the North Side.

One of the few remaining relics of the meatpacking hub that made Chicago the "hog butcher to the world."

An actual 1957 Cadillac De Ville, encased in 15 cubic yards of concrete.

One of the largest pieces of scientific equipment ever carried on a NASA space shuttle sits in a Chicago alley.

The 30,000-volume library is one of the world's most impressive poetry collections.

One-of-a-kind preserved ruins of an abandoned 1880s church in Chicago's Pilsen neighborhood.

Cemetery featuring rare glass-fronted columbarium.

Chicago's North Park Village was once the largest municipal sanatorium in the country.

The only Bahá'í house of worship in North America and one of only a handful worldwide.

A gothic church spire sits atop this skyscraper, the tallest church in the world.

Just your average Marie Antoinette–themed speakeasy in an abandoned 19th-century subway tunnel.

This subterranean spot might be the epitome of Japan's baroque, retro coffee houses.

Step into a cartoon at this Seoul café that aims to evoke a two-dimensional scene.