Crater Lake, formed thousands of years ago from the collapse of a volcano, is famous for its clear blue waters. Summertime visitors can go hiking, swimming, fishing and camping. They can also take boat and trolley tours, go on adventures guided by rangers, explore old-growth forests and wildflower meadows. Climb mountains for stunning views or hike down to the lakeshore itself. For a longer trek, try a backpacking trip on the Pacific Crest Trail.