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

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

L. Frank Baum wrote part of the "Wizard of Oz" series in this wooden Victorian beach resort.

Erosion and various mineral deposits give this striking canyon its distinct color and soft appearance.

A tunnel with windows, so you don't miss out on the impressive views.

The fifth-longest natural arch in the world, and the longest outside China.

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

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

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

The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

Witnessing the might of this dessert-colored desert waterfall is a rare, powerful treat.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

Rippling sand dunes frozen in the Arizona rock.

This long-hidden space above Westminster Abbey now displays the battle gear of the legendary King Henry V.

This museum tucked below a charming cafe gives a brief snapshot of photographic history.

A statue marks the exact spot where The Boy Who Never Grows Up made his first literary appearance.

An small and easily overlooked archaeology museum chock full of Egyptian artifacts.

Where the author wrote her beloved "Little House" books.

Orcas on display and in the water.

This spectacular track has run continuously since 1882.

When ecosystems collide in the arid Southwest.

America's only nuclear missile silo open to the public.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

The remains of this rugged homestead ranch offer a brief glimpse into a bygone era.