The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

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

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

A former major munitions plant that has been converted into a sprawling art space.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

Europe's official "zero-level," the equator of elevation.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

The attic of a four-century-old canal house hides a clandestine church.

A floating cat sanctuary on an Amsterdam canal.

The world's only museum devoted to the wonders of fluorescence.

Hundreds of huge, centuries-old horseshoes adorn the walls of this nontraditional 12th-century castle.

Isaac Newton's former home, where the famous apple tree still stands.

The castle still holds traces of the abandoned Roman fort it was built atop.

Recently restored menagerie of Victorian-era beasts.

A harem-inspired Moorish fantasy design in a Victorian-era Welsh castle.

Brass bricks outline the locations of Edinburgh's lost, lively market stalls.

Edinburgh's oldest statue hides within a parking lot behind the city's iconic cathedral.

The Scottish Reformation leader's grave was paved over and is now a parking lot.

A pair of stones embedded in an Edinburgh street memorialize one of the city's last public hangings.

The 20th-century chapel’s intricate woodwork includes amazing details, most notably angels playing bagpipes.

This alley off Edinburgh's Royal Mile contains remnants of the city's seedier history.