The most accurate timepiece in the world.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

A painfully obvious spy house sits right across the street from the Russian Embassy.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

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

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

An overgrown garden stands as a grim marker of an unrealized dream.

This unique historical monument features large concrete spheres designed to resemble fallen stars.

This grave marks the passing of a historic Jane Doe whose identity remains a mystery to this day.

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

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.

Outsider art meets paleontology at this roadside reptile repository.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

The remains of a failed attempt at medieval nerdery are hidden deep in the woods of Virginia.