A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

This unassuming passageway played a key role in one of the most important events in U.S. history.

When it comes to handsignals (and colonialism) rock always beats scissors.

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

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

A diminutive plaque recalls the treetop sniper who almost killed Abe Lincoln.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

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

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

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

The privately owned cemetery that holds room for Washington's finest when they step down from life.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

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

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

The span is crooked and made from two older recycled bridges.

A clone of a cloned tree that was so important it allegedly had its own guards.

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."

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