Hidden beneath the streets of London is a secret subway that only carried mail.

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

Dr. Strangelove-esque tours reveal the inside a bunker once reserved for Stalin himself.

In this tiny Iranian town playing on the roof isn't just encouraged, it's the only place to go.

This Scottish museum is the only one in the world to focus not on one religion but all of them.

On a site with a long military history, a 1980s shelter.

This disused Cold War bunker has been restored to all of its early 60s glory.

Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

North Korea's massive art and propaganda factory now has an official gallery space in Beijing.

One of the only cooperatively owned bars in the nation wears its eclectic history on its walls.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

The unluckiest U-boat in the entire German fleet is now on display in a Chicago museum.

If you want to talk to the Pope you will have to stare down this surreal vision of Jesus rising from a nuclear hell.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

A museum collection honoring the long history of the FDNY is held in a disused Manhattan fire house.

The National Railway Museum in York is the largest railway museum in the world, attracting almost 1 million visitors per year.

North America's largest accredited model railroad museum.

This museum holds not just a world class collection of firefighting artifacts and gear but even the region's first fire station itself.

This Art Deco fortress in upstate New York gives Manhattan's vaunted examples of the style a run for their money.

The world's only museum devoted solely to the art and collection of action figures.

Opulence and fantasy collide in this royal chair which is supposedly made with unicorn horns.

After this one-of-a-kind palace was built the architect's hands are said to have been cut off to keep it that way.

The largest university building in the West is a gothic masterpiece containing dozens of theme rooms based on different countries.