The strange, ritualistic-seeming 100+ year old basement of a New Hampshire undergrad society.

America's oldest archaeological site or a muddled case of wishful thinking.

In the middle of a New England forest sit the crumbling ruins of World War II-era ammunition storage bunkers.

This mysterious artificial cave has long puzzled New Englanders.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

The French deconstructionist had a weakness for baked goods.

An ultra-modern diversity park in Denmark has turned an entire city block electric pink.

Bizarre lunar-like landscape with thousands of large stone "hoodoos."

Neon artworks light up this dark Edinburgh tunnel.

Traveling collection of amazing automata.

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

This little museum is making sure that the art and history of the graffiti sticker is not scraped from history.

Machinery left over from California's once thriving mercury industry now attracts artists and explorers.

This colorful but controversial ceiling has been likened to a 21st-century Sistine Chapel.

Vast network of air raid tunnels beneath Lombardy's capital.

The secret medieval communication system will whisk your words above the noise of the crowd.

A Milanese café entirely designed by the American director Wes Anderson.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

On the Oregon coast there is a natural hole that seems to be draining the sea.

This volcanic cave lake is essentially hard proof that Iceland is the most magical place on Earth.

100-windowed castle turned art gallery, built by one dedicated mason.

This French "sea of rocks" is packed with stunning rock formations and its own medieval castle.