Michigan's Remote and Wild Isle Royale National Park

Hiking on the islands is popular because of their rugged and unique terrain. North-south trails continually rise and fall over a series of ridges and troughs; the Greenstone Ridge Trail, on the other hand, remains relatively level as it traces a high east-west ridgeline across the island as much as 600 feet above the lake.

This unusual washboard topography began forming some 2 billion years ago, a product of spewing volcanoes, colliding continents and seeping lava flows.