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

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.

A line of blue paint marks the route of the inaugural parade.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

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

An overlooked memorial honoring the local Washington residents who died in World War I.

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

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

Largest Roman Catholic church in North America.

A museum designed by and dedicated to P.T. Barnum in the town where he is buried.

The US Navy's only submarine museum is also home to the world's first nuclear submarine.

The mysterious headstone of an unidentified bank robber was seen visited, every year, by a woman in black.

Quirky castle designed by the American actor best known for portraying Sherlock Holmes on stage.

This opera house along the banks of the Connecticut River has two Tony Awards to its credit but it’s never staged a single opera.

The Connecticut village named for its subterranean thunder.

This stately monument has been wearing a traffic cone hat for decades much to the delight of the locals.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

After it was swallowed by a Georgian mansion, this medieval castle remained forgotten for centuries.

One of Ireland's most infamous prisons for rebels including men, women and children.

An Irish church where an 800-year-old mummy is reaching out of his coffin as if to shake hands.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

This early version of the guillotine was used to execute the man responsible for its construction.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.