Salute the leader of the proletariat.

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

The oldest family-run luncheonette in New York, last renovated in 1948, still serves food and drinks the old-fashioned way.

A hidden "place of interment for gentlemen."

A good place to research the Freemasons, esoterica, occultism, and hermeticism.

Cryptic messages embedded in the New York City sidewalk.

Unlock the secrets of the conjuring arts.

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

A New York garbage depot holds a secret collection of weird and wonderful refuse.

On the top floor of an upscale department store stands a lavish restaurant housed in a replica of a luxury French dining car.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

New York City's smallest piece of private property.

New York's oldest magic store.

Tucked in the back of this amazing antique store is an important piece of medical history.

A crumbling hospital from the 1850s on Roosevelt Island.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

A century-old shot ball factory tower is open to the public once a year.

A traditional U-Bahn station in Berlin gets a string of rather untraditional benches.

After a nearly successful attempt on Hitler's life, the conspirators met their fate in the courtyard of this Berlin building.

This conical hill was built as a testing ground for an engineer known as the Glider King.

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

From toys to kettles to scientific instruments, this German museum celebrates the beauty of 20th century design.

A state-of-the-art medical facility from the Imperial era is now a derelict ruin.

The music is over at the Ballhaus Riviera Ballroom, but the ballroom remains in haunting disrepair.