Oregon’s Crater Lake, America’s deepest lake, is also arguably its bluest. Fed entirely by rain water and snowmelt, this natural wonder and centerpiece of Crater Lake National Park was formed after the explosion of an ancient volcano—Mount Mazama—about 7,700 years ago. Volcanic features dot the landscape around the lake, including the Pinnacles, a set of now-cooled pumice spires that were once channels for underground steam and gas. The 33-mile Rim Drive encircles the lake, while a bevy of hiking trails offer access to various viewpoints, canyons, and waterfalls. Visit in summer or early fall, as snowpack leads to road closures during much of the rest of the year. (Note: For more information, see the Crater Lake National Park Guide.)