I stayed at this campsite the night before my group and I climbed up to Helen Lake to setup basecamp. I got to the trailhead around 3:30 and hung out around the area. The rangers are amazing, super friendly and offer a lot of information about the climb. There are campsites all over the place, but I stayed in my car so I don't have any information about the sites themselves. You have unreal views of Mt Shasta and when I was there the gate was locked to go up to Old Ski Bowl so I took my bike to go check it out. It was super cool!
This is honestly one of the best state park camp grounds I have ever been to. The rangers are amazing, the trails are even better, and the views are breathe taking. With it being only a couple miles off of the highway, great for staying while you're on those long hour days in the car, it allows for you to get away while also being super close. I ran to the observation point, which was great but I did see a small black bear. It ran off but just note there are bears in the area and you need to store your food properly.
Anywhere you go on the Cascades Lake Highway is amazing, views that go on for hours of the mountains. This campsite allows you to be engulfed in these views for however long you want. Directly across the lake you get views of Mt Bachelor, South Sister and Broken Top. In the early season its very buggy and I would suggest bring a lot of bug spray, it kinda helps. The facilities are clean and well kept. I would suggest waiting to come here until around August when all of the bugs are gone but the views are absolutely spectacular!
I was on a solo road trip this last week and was searching for campsites near Crater Lake and I stumbled upon Diamond Lake. I really like how they have two loops dedicated to first come first serve, thats pretty cool. I got a spot right along the water, bugs weren't bad, and the sunset was amazing that night. The camp staff are super inviting and are pretty awesome! I had an amazing night at the campsite.
The surrounding area is great for recreation, bring your bike and cycle the loop that goes around the entire lake. You get mountain views the entire time. There are loads of hiking, ask the camp staff for trail maps. There is apparently great fishing but I didn't have fishing license.