Cavern in Pictured Rocks National Lakeshore on Lake Superior, USA

© Kenneth Keifer/Getty Image

At the shore of an inland sea

We're looking out from a cavern at Pictured Rocks National Lakeshore in Michigan's Upper Peninsula (Midwestern United States). The area's named for its colourful sandstone cliffs, which stretch for 24 kilometres along the shores of the largest of the Great Lakes of North America, Lake Superior. As groundwater leaches out of the rocks, it carries minerals such as iron, manganese, and copper that paint the cliffs in shades of red, pink, black, green, and other colours. The park itself boasts waterfalls, beaches, and rock formations—some resembling human profiles and castle turrets—carved over time by the relentless waves and unforgiving weather of the region.