7. Crater Lake – Oregon, USA

Crater Lake’s intense blue waters are a sight to behold. Formed within the collapsed caldera of Mount Mazama, this lake boasts remarkable clarity thanks to its isolated ecosystem—no rivers in or out. You can take a boat tour to Wizard Island or hike the rim for stunning perspectives. Swimming is allowed in designated areas, but be warned: even in summer, the water is bracingly cold. Crater Lake is pure, untouched natural beauty at its best.