Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

St. Mary's features one of the most spectacularly decorated cathedral interiors in all of Europe.

An underground city of salt.

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

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

Perhaps the most scandalous statue of America's first president.

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

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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

The walls of the iconic dome are hollow and have a secret stairway.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

A gorgeous mural outside a beloved D.C. restaurant pays homage to famous Black Americans.

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

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

Look closely and you’ll notice that the color changes a third of the way up the tower.

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.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.