A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

The first memorial dedicated solely to the Black troops who fought for the Union.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

The "lovely red Vega" of the legendary record-settling pilot.

Washington's iconic carousel has a nice piece of Civil Rights history.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

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.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

Roses and other fascinating flora fill this garden built to commemorate Britain's immortal Bard.

Half-sized replica of the Leaning Tower of Pisa built to honor Galileo.

Where a brain, a beauty, a jock, a rebel, and a recluse met one Saturday and changed their lives forever.

The palatial McDonald's that inspired Wesley Willis.

The last masonry skyscraper ever built reveals a transitional moment in architectural history.

A spectacular remnant of an Adler and Sullivan masterpiece that was destroyed in 1972.

G.V. Black, the Father of Modern Dentistry, keeps an eternal eye on Chicagoan’s teeth from his perch in Lincoln Park.

Huge abstract sculptures of the Puerto Rican Flag.

A 19th-century horse lover's bequest led to the construction of this unique fountain in Chicago.

The original Garfield station is the oldest station facility on the "L", with the station house dating from 1892.