An acoustic anomaly with a mysterious cause.

This lovely pocket park is one of the most under appreciated in D.C.

The oldest continuously operating fish market in the United States.

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

Home to items never before seen by the public.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The "lovely red Vega" of the legendary record-settling pilot.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

A much-maligned monument to teetotalism.

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

The sculptor was instructed to add “stallion attributes” to the general's bronze mare.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

D.C. once had its own tiny rival to the New York Stock Exchange.

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