Golden Gate Park's historic collection of plants.

Quite simply the largest tree in the world (by volume).

Inside this library, the history of Los Angeles is retold through a mural.

This nondescript tunnel has been featured in a number of iconic movies, from “Roger Rabbit” to “Back to the Future.”

The decor of this Hollywood movie palace just barely predated the opening of King Tut's tomb.

A luxury hotel constructed out of a former jail.

This hotel was the site of major events in sports and radio history. It was also used as a detention center during World War II.

This historic Boston building has gone from personal estate to porn theater and back again.

The former site of an all-but-forgotten colonial landmark is now remembered by an often overlooked bas relief.

Historic Hull Street was actually the first street with a proper name in the Boston area.

This ambitious father and son team reigned supreme over the North End, and witches, for many years.

The history of the tea trade is told in bas-relief on this historic pair of Boston doors.

The Boston square dedicated to the dark poet who was born nearby.

A city park that sits on top of a freeway.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

This bridge over D.C.'s Rock Creek Park is sometimes called the "Buffalo Bridge" because of its four buffalo sculptures, which were cast from a single piece of bronze.

The last remaining building in Washington, D.C., built by H.H. Richardson, one of America's most iconic architects.

Outside the Department of Transportation, a collection of artifacts honors the history of how we get around.

A secret greenspace hides atop a Capitol parking garage.

Corn-inthian columns with a uniquely American take on neoclassical architecture.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

100 years later, they're still down there.