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

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

Architectural monsters are devouring this palace's every door and window.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

The world's longest known cave system.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

A beautiful geyser under environmental threat.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

The first declared National Monument in the United States.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

Paranormal experiences in this hotel's room 217 led Stephen King to write "The Shining."

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

These two monoliths have stood at the entrance to the neighborhood since the days it was called "Hollywoodland."

The blinking light atop the iconic landmark has been sending secret messages for decades.

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

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

Largest Roman Catholic church in North America.

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

Tirelessly maintained by a Wisconsin man named JFK.

A haunting army of decomposing, moss-covered stuffed animals and dolls guard this swinging truss.

One of corporate America's best-kept secrets is also one of the most publicly displayed.