An architect's childhood fantasy treehouse made real.

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

A beautiful geyser under environmental threat.

The first declared National Monument in the United States.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

Largest Roman Catholic church in North America.

A wall of chewing gum moonlights as collective art.

A giant Troll lurks under one of Seattle's oldest bridges.

Walk the whole Mississippi River!

The hotel where Martin Luther King Jr. was shot is now a museum dedicated to his work.

All that's left of the quintessential "cabin in the woods."

A fitting attraction for the corn capital of the world.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

What was meant to be a temporary exhibit is now a permanent fixture at the St. Louis Zoo filled with beautiful birds.

Speak to a companion on the other side of the room loud and clear through this architectural anomaly.

What was once a presidential estate is now an exotic menagerie and home to the Budweiser Clydesdales.

Less a museum than a bizarre fantasy world created by artists and engineers.

Downtown Minneapolis mixed art and function by turning some of their sewer covers into works of art.

Equal parts record-breaking temple to consumerism and bizarre fun park, it's more than you think it is...

A toweringly silly piece of modern art has been delighting locals since the 1980s.

20,000 pieces in a Frank Gehry-designed building.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

This national park on the shore of Lake Michigan features remarkable dunes that lie at the heart of a Chippewa legend.

This four-story steel sphere in Maryland was used to test biological weapons.