Crater Lake, formed thousands of years ago from the collapse of a volcano, is famous for its clear blue waters. Summertime visitors can go hikingswimming, 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.