This pseudo-steampunk weapons facility is the world's largest wood and glue structure, and packs quite a wallop.

Rippling sand dunes frozen in the Arizona rock.

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

A historic ruin just 20 feet away from a busy highway onramp.

An Industrial Revolution-era public work that purified water using nothing but sand.

A haunting tribute to pioneering photographer Clover Adams.

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

This dig site outside D.C. is known for its exceptionally high density of baby dinosaur fossils and dinosaur eggs.

A sealed test tube said to hold Thomas Edison's dying breath was given to the inventor's friend and mentee, Henry Ford.

Outsider art meets paleontology at this roadside reptile repository.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.