People escaping slavery may have hidden inside a corpse vault.

The tunnel under the Capitol Building where Congress takes out its trash.

The walls of the iconic dome are hollow and have a secret stairway.

During Prohibition, the U.S. Congress had an "official" bootlegger, with his own Capitol Hill office.

A nostalgic bibliographic gem.

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

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

The ruins of the "20-year town" lay out among the mountains of Alberta.

The only way to visit this old resort hotel is with scuba gear.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

Canada’s surprisingly controversial monument to Dwight Eisenhower.

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

The oldest continuously operating fish market in the United States.

A much-maligned monument to teetotalism.

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

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

The most accurate timepiece in the world.

A historic neighborhood church is reborn as a psychedelic arts collective.

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.

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

This lovely pocket park is one of the most under appreciated in D.C.

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

The walls of Germany's Parliament still show the scars of the Red Army takeover in World War II.

The wooded estate of the Forest Service employee responsible for D.C.’s cherry blossom trees.