The plants form a living library and laboratory for researchers and students at Michigan State University.

The honor of highest point in Michigan was almost given to the wrong peak before this mountain won out by 11 inches.

This observatory comes complete with three separate telescopes and a dedicated community of amateur and expert astronomers.

These sprawling mines once served as a source of plaster and today serve as a storage facility.

World's largest Christmas store.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

The most accurate timepiece in the world.

Obscure Freemasons still live in D.C.’s largest private residence.

Decades before the scandal, this staircase on the river was a literal "water gate."

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

A computer bug so primitive it was an actual insect.

There's a crumbling old mansion inside the Smithsonian National Zoo.

An Industrial Revolution-era public work that purified water using nothing but sand.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

The house where John Wilkes Booth conspired with his co-conspirators.

The famous abolitionist’s preserved estate is one of Washington's finest monuments to its great Black citizens.

The oldest continuously operating fish market in the United States.