Waipio Valley ( Hawaii )

Waipiʻo Valley is a valley located in the Hamakua District of the Big Island of Hawaiʻi. "Waipiʻo" means "curved water" in the Hawaiian language.

A steep road leads down into the valley from a lookout point located on the top of the southern wall of the valley. The road gains 800 vertical feet (243.84 m) in 0.6 miles (0.9 km) at a 25% average grade, with steeper grades in sections. This is a paved public road but it is open only to 4 wheel drive vehicles. If classified as a road, it would be the steepest road of its length in the United States and possibly the world.