Visible below the waves are memorials to the city's Gold Rush dead.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

San Francisco's newly reopened hands-on science museum.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

This crumbling industrial fortress has attracted daredevils, filmmakers, and historians.

Designed by Buckminster Fuller, this relic of the 67 Expo survived fire and ice.

This 1967 experiment in modular architecture was designed to be a new model for urban living.

A line of blue paint marks the route of the inaugural parade.

An overlooked memorial honoring the local Washington residents who died in World War I.

Look closely and you’ll notice that the color changes a third of the way up the tower.

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

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

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

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

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

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

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

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

This "life-size" depiction of Mickey Mouse as a half-lobster is both whimsical and a bit creepy, standing guard over the Boston waterfront.

The massive machine creates cracking displays of indoor lightning.

A 400-foot-tall tall map of Chicago makes this once-ignored building stand out.

Chicago's Navy Pier on Lake Michigan was a training hub for aircraft carrier pilots during WWII.

These chunky stone towers out in Lake Michigan are the key to Chicago’s drinking water.

The unluckiest U-boat in the entire German fleet is now on display in a Chicago museum.