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

A double agent hid information for the Soviet Union beneath this bridge for more than 20 years.

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

Politicians, bureaucrats, and military officers gathered in this field near the Capitol to settle their disputes with blood.

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

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

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

One of the only memorials dedicated to journalists who died in combat.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

This Virginia railway overpass is said to be haunted by a serial killer in a rabbit costume.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

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

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

This might just be the TARDIS of bookstores.

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

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

An FDR-era tuberculosis sanatorium has stood abandoned in the suburbs of the U.S. capital for over 30 years.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

This simple stone memorial remembers a secret, Geneva Convention-defying interrogation base from WWII.

Parking garage where Bob Woodward met Watergate source "Deep Throat."