The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

A Texas cave network is home to some of the world's most spectacular-looking and bizarrely named mineral formations.

These towering spires and glowing walls are carefully crafted from hundreds of thousands of icicles.

Mile-long cave system near Great Smoky Mountains.

Dig for your own trilobites in this goldmine of invertebrates.

A well-preserved Ancestral Puebloan ruin tucked beneath a desert cliff.

These Pre-Columbian petroglyphs contain representations of birds, deer, hunters, and even some early Native flute players.

This massive redwood tree has a hole in the base big enough to drive through.

This replica of the Greek structure is in the heart of Nashville.

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

Mysterious ancient boulder carved with petroglyphs in the mountains of Western North Carolina.

The Grand Canyon of Texas.

The second largest waterfall by volume in the U.S., Willamette Falls is outdone only by Niagara in the amount of water that is pushed northward.

Who needs fancy modern water slides when this giant North Carolina rock works just as well?

A wall of chewing gum moonlights as collective art.

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

A modern mechanical planetary system, part of a 10,000 year clock.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

A shop full of natural curiosities, carnivorous plants, and costumed taxidermied mice.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Ruins of the elaborate house where the enigmatic costume designer threw glamorous parties for New York's theatrical elite.

Oregon's unexpected high desert, displaying layers of time in a colorful show.