A bunker "with enough U.S. currency to replenish the cash supply east of the Mississippi" in the event of nuclear war now protects nitrate film.

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

A local farm's collection of unusual structures from a now defunct storybook amusement park.

A remote horde of architectural treasures fit for Indiana Jones.

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

A priceless collection of the Nation's cryptologic history.

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

The development and impact of electronic media showcased in a picturesque farmhouse in Maryland.

The U.S. government built the million-pound stack of steel during the Space Race.

This golfball sized platinum iridium cylinder is the official starting point for all national weight calibrations

A haunting exhibit in a wildlife refuge center highlights threatened species and the conservation efforts needed to save them.

This dig site outside D.C. is known for its exceptionally high density of baby dinosaur fossils and dinosaur eggs.

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

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

An FDR-era tuberculosis sanatorium has stood abandoned in the suburbs of the U.S. capital for over 30 years.

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

A double agent hid information for the Soviet Union beneath this bridge for more than 20 years.

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

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

A mammoth pair of Civil War artillery guns abandoned out in the forest.

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

An astounding collection of medical specimens, including bits of President Lincoln.

Once home to seven different roller coasters, Glen Echo has undergone many transformations since its founding in 1891.

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