This scenic Maryland park was the site of one of the worst prison camps of the Civil War.

A cave on the Maryland border where civilians took refuge during the bloodiest battle of the Civil War.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

Scattered throughout London are ancient remnants of the city's former bounding wall.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

Collecting 700 years of mechanical death-dealing, the NRA's sprawling gun museum is a revealing testament to the American obsession with armament.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

The final resting place of many of New Jersey's most famous residents, including U.S. history's most in-vogue antagonist, Aaron Burr.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

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

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

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

After a nearly successful attempt on Hitler's life, the conspirators met their fate in the courtyard of this Berlin building.

Largest lake in Great Britain measured by surface area.

Overlooking a Scottish loch, this beautifully crumbling castle once inspired a poem by William Wordsworth.

The last bastion of Roman presence north of the Alps looms over a German town.

A star fort along the C&O Canal in western Maryland that protected America in three wars.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

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

An unusual round church in London with a Templar past.