This huge, disused viaduct is now a crumbling concrete underworld of covered in years of graffiti.

The largest collection of Frazetta originals in the world.

One of the U.S. Forest Service's only mansions is outfitted with a dinner table for floating food.

The shelves in the back of this thrift store are devoted to saving, not selling, retro tech.

This mighty white oak in Bethesda survived both the American Revolution and the construction of Washington D.C.'s metro red line.

Although built to generate electricity for Marylanders, this dam has become an all-you-can-eat buffet for American bald eagles.

A total of 14 men held the title of "president" before George Washington—their historical legacies are enshrined in the lobby of a hotel.

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.

The Decoy Capital of the World.

Its diverse collection of computers and technology spans the ages.

Surrounded by traditional homes, this Tolkien-esque dwelling stands out on a quiet street in suburban Maryland.

The world's oldest continuously operating airport was founded by the Wright Brothers.

This suburban house is made of dirt, and almost sparked a revolution in home construction.

Electronic inventions that resulted in products and systems we use every day are on display in this labor-of-love museum.

A lawn full of retired spacecraft on display at one of NASA's first research labs.

The Forest Service's surprisingly sophisticated collection of wildfire prevention art features America's most beloved bear.

Walk a trail through a historic Quaker town that outlawed slavery in 1777 and was a major waypoint on the Underground Railroad.

An intricately designed junk art house with four extravagant junk art cars hidden in the suburbs.

This English-inspired Maryland garden is home to acres of opulent plant life including bushes shaped into an entire fox hunt.

Bizarre Cavern.

The land is home to swimming ponies and a legendary 18th-century treasure.

A suburban museum tells the story of a historic transportation network and even provides rides in antique trolley cars.

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