Jesus' footprints and the first catacombs in the world.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The final resting place of the poets Shelley and Keats.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Architectureal fantasy quarter of Rome.

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

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

This unique museum cafeteria showcases the history and regional diversity of African American cuisine.

Sit where JFK proposed to Jackie or where Nixon dined on meatloaf at this storied pub.

This restaurant has been a haven for D.C.'s LGBTQ community since the 1950s.

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.

A celebrity from the late Cretaceous period.

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

An Industrial Revolution-era public work that purified water using nothing but sand.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A derelict bit of transportation infrastructure hidden in the woods.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A wondrous old library overlooking the nation's capital.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.