This upscale streetwear store is hidden behind a fake Snapple machine in the back of a deli.

The old Niles Canyon Aqueduct in the San Francisco Bay Area is a bemusing and secret trail through nature for wayward travelers.

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

Scattered throughout London are ancient remnants of the city's former bounding wall.

These curious caverns have been home to mushrooms, gangsters, and disco.

An architect in Aspen used psychedelics as his muse while building this mushroom masterpiece.

This massive mushroom has spent centuries eating its way across a huge swath of Oregon.

Covering 37 subterranean acres, this Armillaria gallic is a famous fungus with its own festival.

More gold than anywhere else, ever.

A hands-off space for graffiti artists to hone and display their skills.

Jesus' footprints and the first catacombs in the world.

Stay in a room with a view... of the bottom of the ocean.

Beautiful carved tunnels.

Fantastically decorated underground chambers built in the 1760s.

This museum celebrating the almighty dollar lets visitors literally stand in the shadow of a million bucks.

Beyond being incredibly fun, not much can be said about the Hole with certitude.

Hunt for buried treasure in Nova Scotia.

Rebuilt remains of a temple to Roman god Mithras.

Why have you never heard of the second most popular tourist site in New York?

After Havre burned down, the best place to build was under the ashes.

The kind of mixed-up place that drives archaeologists crazy.

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

The underground sanctuary of a mysterious ancient cult.

In the middle of downtown Brooklyn lies a 165 year old secret hidden right below the surface (closed to the public indefinitely).