Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

The most accurate timepiece in the world.

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

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

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

This one has sailed five times as far as Sir Francis Drake's famous ship.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

Live data is transmitted from the Atlantic coast to instantly recreate the ocean waves in this fountain at the NOAA headquarters.

A celebrity from the late Cretaceous period.

The final resting place of the great navigator, or maybe his brother.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

Louise Bourgeois' 30-foot-tall steel spider sculpture.

Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

This bug-eyed water wheel uses the power of the Sun to clean up Baltimore Harbor.

The 16th-century church has the only stained glass windows that survived the Scottish Reformation intact.

The oldest still-operating tavern in the United States was once owned by a pirate.

A beautiful ruin of a 14th-century Plantagenet castle built by a medieval mercenary.

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

Three and a half miles of cliffs, rocky beaches, Gilded Age mansions and 40 Steps to nowhere in particular.

Home to a vast and influential collection of Shakespeareana.

A relic of Victorian grandeur hides beneath a busy South London road.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.