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

Perhaps the most scandalous statue of America's first president.

Washington's iconic carousel has a nice piece of Civil Rights history.

The national park was once a plantation estate.

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

Decades before the scandal, this staircase on the river was a literal "water gate."

The oldest continuously operating fish market in the United States.

The most accurate timepiece in the world.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

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

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

The walls of the iconic dome are hollow and have a secret stairway.

A nostalgic bibliographic gem.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

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

Home to items never before seen by the public.

The site of the climactic scene from the classic horror film is now a historic landmark.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

This one has sailed five times as far as Sir Francis Drake's famous ship.

Rebuilt remains of a temple to Roman god Mithras.

An incarceration museum on the spot of possibly the oldest prison in England.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.