The first declared National Monument in the United States.

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

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

The self-made house sculpture of an outsider artist who named himself "Chief Rolling Thunder."

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

Come for the speed, leave in love with the desert.

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."

This ancient spring in central London was featured in a Peter Pan story.