The 320-year-old tree that greeted General Lafayette and rerouted an interstate highway.

Remnants of a storybook amusement park hidden behind a strip mall.

The headquarters of the Audubon Naturalist Society is a small slice of heaven for nature lovers.

One of the oldest active carousels in the country—but it might be missed by all but the keenest-eyed boardwalk strollers.

A state park that once served as an important river crossing, and now offers protected lands for endangered plants and animals.

The 72-foot giant escaped confinement in a large patch of mulch only to be reburied in the sandy shores of the Potomac River.

Tiny observatory made big contributions to the study of the Earth's motion.

Once part of a dam servicing an early 19th century grist mill, the tucked-way falls are a tricky-to-find urban oasis.

A swimming hole in the historic industrial quarry that supplied the marble for the Baltimore Washington Monument.

This historic lighthouse was well known for the large number of women who served as its keeper.

A benevolent, 16-foot-tall river dragon lives on a suburban lawn.

Dogs, cats, horses, monkeys, frogs, and fish are laid to rest at the second-oldest pet cemetery in the U.S.

Politicians, bureaucrats, and military officers gathered in this field near the Capitol to settle their disputes with blood.

Rediscovered after a century, the father of the American Navy was reinterred in something dredged up from Davy Jones' Locker.

The whole world in one water tank.

This beautiful stone arch bridge wasn't even expected to stand for one day, but people have been crossing it for centuries.

Brain collection and database that narrows the gap between man and animal.

A labor of love built by local hang-gliding enthusiasts, this ideal launch spot was outlawed by the authorities and has since been largely abandoned.

A remote horde of architectural treasures fit for Indiana Jones.

This scenic Maryland park was the site of one of the worst prison camps of the Civil War.

Live data is transmitted from the Atlantic coast to instantly recreate the ocean waves in this fountain at the NOAA headquarters.

The final resting place of the tragic king and queen of the Jazz Age is tucked away in a small Maryland graveyard.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

A cave on the Maryland border where civilians took refuge during the bloodiest battle of the Civil War.