The Apostle Islands are a twenty-two-island archipelago in Lake Superior off northern Wisconsin, with all but Madeline Island included in Apostle Islands National Lakeshore. Formed from ancient sandstone shaped by erosion, storms, and possibly water beneath continental ice, they are known for dramatic sea caves that can fill with ice in winter. The islands also support rich biodiversity, including boreal forest, rare plants, bog dune ecosystems, black bears on Stockton Island, and a great blue heron rookery on Eagle Island. For thousands of years the region has been important to Indigenous peoples, especially the Ojibwe, for whom Madeline Island holds deep sacred significance.