Infrastructure in Washington, D.C.

This bridge over D.C.'s Rock Creek Park is sometimes called the "Buffalo Bridge" because of its four buffalo sculptures, which were cast from a single piece of bronze.

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

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

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

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

These abandoned waterworks are crumbling into the Potomac River.

The tunnel under the Capitol Building where Congress takes out its trash.

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

A derelict bit of transportation infrastructure hidden in the woods.

100 years later, they're still down there.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

Every drop of D.C. tap water flows through this old waterworks.

The most accurate timepiece in the world.

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