An eerie smiling woman looms above the granite tombstones.

"X" marks the spot of an echo chamber in the middle of a plaza.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

The highest point in Maryland is only accessible by hiking through another state.

Two gems of Beaux Arts architecture that have been sitting vacant for years.

Baroque celebration of the end of the Great Plague of Vienna.

Legends surround an ancient tree trunk riddled with nails for good luck.

At 207 feet, one of the world's longest continuous escalators.

Home to items never before seen by the public.

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

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

Exact replica of the ancient monument, but much, much lighter.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

Edgar Allan Poe's old dorm is now a shrine to the author's legacy.