The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

The Forest Service's surprisingly sophisticated collection of wildfire prevention art features America's most beloved bear.

Two dozen pinball games hidden away inside a most unlikely location.

This suburban house is made of dirt, and almost sparked a revolution in home construction.

The wooded estate of the Forest Service employee responsible for D.C.’s cherry blossom trees.

America's first federal monument.

A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.

An intricately designed junk art house with four extravagant junk art cars hidden in the suburbs.

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

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

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

This forgotten boat elevator was an engineering marvel in its heyday.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

A building shaped like the Army Corps of Engineers logo, because why not?

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

A painfully obvious spy house sits right across the street from the Russian Embassy.

Bar full of oddities, specimens, artifacts and homages to the great dime museums of the past.

Giftshop catering to cryptozoologists and anyone with a sense of humor.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

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

The Pentagon sits on a former island that was in Virginia at low tide and D.C. at high tide.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

100 years later, they're still down there.