A popular swimming hole that hides one of America's most deadly diving spots.

An emerald-green grotto just a short trip from Austin.

The ruins of Theodore Roosevelt's beloved ranch stand in a forgotten corner of a national park named after him.

A warning to the weak-kneed: This narrow bridge does its swinging eight stories high.

The world's longest known cave system.

This sprawling bookstore spans four floors and has more than a million books in stock.

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

Two hundred tons of pioneer artifacts were painstakingly recovered from a shipwreck at the bottom of the Missouri River.

The only diamond mine in the world where you can keep what you find.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

This pole near the infield rail at Belmont Park marks the jaw-dropping margin of Secretariat’s 1973 Belmont Stakes victory.

A prized globe signed by Amelia Earhart and Charles Lindbergh sits in the Brooklyn office of the American Geographical Society.

The world’s largest collection of Tiffany glass sits in a warehouse in Queens.

The original toys that inspired the beloved children's stories are on display at the New York Public Library.

Mysterious 500-year-old tapestries depict a unicorn hunt.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

A crumbling hospital from the 1850s on Roosevelt Island.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

This narrow canyon has been carved by the river over thousands of years into spectacular and curious forms.

Even Henry David Thoreau found this glacial pothole irresistible.

The first declared National Monument in the United States.

Gorgeous cave resemble a winter wonderland.

The king of U.S. high points towers over every other peak on the continent.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.