This hidden gem of a garden has one of the only surviving Victorian ferneries in America.

Bizarre Cavern.

This grave marks the passing of a historic Jane Doe whose identity remains a mystery to this day.

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

A wondrous old library overlooking the nation's capital.

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

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

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

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

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