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

One street divides a single town that stands in two U.S. states.

At 207 feet, one of the world's longest continuous escalators.

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

The resting place of a Civil War celebrity's amputated limb.

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

Heron, whitewater rapids, and urban industrialism all add to the beauty of this concrete nature walk.

A railroad tunnel that, upon its completion, was considered one of the engineering marvels of the modern world.

Exact replica of the ancient monument, but much, much lighter.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

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

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

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

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

The national park was once a plantation estate.

There’s a hidden military meme engraved on the World War II Memorial.

A nostalgic bibliographic gem.

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

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

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

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.