Hundreds of antique bank vault locks on display in New York City.

The world's oldest hologram gallery and the labyrinthine laser laboratory of a holography pioneer.

The first museum in the United States dedicated entirely to posters.

This hidden library of physiological ephemera contains centuries worth of knowledge on the vim and viscera of the human body.

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

30 years worth of pressed-tin, bakalite, and characters both loved and forgotten.

This Russian locomotive museum was once devoted just to Lenin's funeral before expanding to encompass Moscow's entire train history.

Immortal combat in a Moscow museum.

This hidden park hosts a rogue’s gallery of eccentric architectural obelisks.

Two adjoining collections of 19th-20th century physics apparatuses and instruments.

Small museum dedicated to the founder of electromagnetic theory.

This stately bank building hides a spectacular star-studded ceiling.

The U.K.'s first underground railway line is now a lively thoroughfare for runners and cyclists.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

This obscure walkway links Edinburgh’s Old Town with one of the city's prime vantage points.

Tiny effigies of the victims of Edinburgh's famous Anatomy Murders.

During the solar phenomenon "Lahaina Noon" this bendy, curvy sculpture forms a perfectly circular shadow on the ground.

Strolling through these vintage locomotives offers a surprising amount of insight into the history of Kenya.

Apple memorabilia in an undisclosed warehouse, hidden for undisclosed reasons.

Four miles of pipelines form the model of still-functioning retro-tech efficiency.

If you want to build a better mousetrap, first consult this small museum's massive collection of trapping tools.

This whimsical campus lawn is dotted with large sculpted numbers and hidden mathematical formulas.

Known locally as "the giant head," this 14-foot LED sculpture has a photo booth in the neck where you can have a 3D picture taken and displayed.

Celebrating the history of Hangul, the Korean writing system invented by King Sejong to improve his realm’s literacy.