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

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

Where the U.S. government kept its actual treasure, before Fort Knox.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

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

A computer bug so primitive it was an actual insect.

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

People escaping slavery may have hidden inside a corpse vault.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

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

A nostalgic bibliographic gem.

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

A wondrous old library overlooking the nation's capital.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

This grand gothic brewery has been pumping out suds for over a hundred years.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.