Largest Roman Catholic church in North America.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

A nostalgic bibliographic gem.

When it opened during the final years of the embargo, all the drinks and cigars were free.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

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

A derelict bit of transportation infrastructure hidden in the woods.

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

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

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

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.

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.

Home to items never before seen by the public.

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

The resting place for anonymous victims of the Danube's dark waters.

This cubist Vienna church building looks like some sort of alien stonehenge.

Op-art architecture designed for happiness.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

Climb to the top of this spiritual tower, and you'll be rewarded with spectacular views.