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

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

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

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

A clone of a cloned tree that was so important it allegedly had its own guards.

This unique museum cafeteria showcases the history and regional diversity of African American cuisine.

The world's oldest soul food restaurant is also one of its best.

One of two giant blue cockerel statues erected with an intentional double meaning.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

When it opened during the final years of the embargo, all the drinks and cigars were free.

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

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

There’s a hidden military meme engraved on the World War II Memorial.

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

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

People escaping slavery may have hidden inside a corpse vault.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

A derelict bit of transportation infrastructure hidden in the woods.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

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

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.