This Philly landmark has a giant butterfly pavilion, three floors of insect displays, and withstood a $40,000 heist.

Instruments, apparatus, and rare books all relating to chemistry and its related sciences.

This little-known Revolutionary War fort is supposedly haunted by the ghosts of its past.

A rare view of a preserved Victorian science museum.

Tour the dark and beloved poet's former cobwebbed basement, which may have inspired "The Black Cat."

Where America's first doomsday cult awaited the end of the world.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

World's first "penitentiary," meant to be humane, drove men insane.

A desiccated merman and a walrus penis bone are among the oddities in this eclectic collection of shipwreck treasures.

This collection of odd proofs of concept is like taking a walk through the imagination of a Victorian engineer.

This splendid Versailles-inspired mansion has the largest French-style formal gardens in North America.

Enchanting gardens surround a derelict mansion, all hidden in plain sight behind a stone wall.

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

Art deco landmark on the outskirts of Washington, D.C.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

The oldest continuously operating fish market in the United States.

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

Home to a vast and influential collection of Shakespeareana.

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

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

The most decorated dog of World War I is preserved in the Smithsonian.

The walls of the iconic dome are hollow and have a secret stairway.