This beautiful, deep-blue lake attracts motorboat and RV enthusiasts in summer, with activity centered on a bustling full-service resort. There are fishing, boating and swimming possibilities, along with a 12-mile paved bike path around the lake. Winter brings cross-country skiers.
Rising to the east of Diamond Lake is pointy Mt Thielsen, a 9182ft basalt spire. A 5-mile trail (10 miles round-trip; Northwest Forest Pass required or pay $5 on-site) begins 1 mile north of the junction of Hwys 138 and 230 and stops 80ft short of the summit, which is attainable only with technical climbing skills.