This nine-story building is the oldest standing skyscraper in D.C.

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

A portal into the bricked up canal that runs through the heart of Washington D.C.

The only tennis court that falls under the jurisdiction of the central bank.

Right next to departures—how convenient!

The hidden offices underneath Memorial Bridge have been locked up since 1976.

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

The U.S. Fish Commission’s effort to mass produce carp.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

A derelict bit of transportation infrastructure hidden in the woods.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

There’s a special club house at the top for the bell ringers.

A line of blue paint marks the route of the inaugural parade.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

The elevator that makes it possible to fly American flags in bulk over the U.S. Capitol

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

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

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

Once at the center of U.S. finance, the historic Trading Room was meticulously recreated piece by piece and rebuilt in the Art Institute.

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

This $3 million model train takes you through Chicago, Seattle, and the thousands of miles in between.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.