We stayed in the Mazama Village Campground, inside the park and about seven miles from the lake rim. We have found that it is easy to stay in the park campgrounds on these short trips. The campground has water and showers.
Crater Lake is spectacular, with good hiking trails, a beautiful drive around the rim of the lake, and an historic lodge. There is nothing like going up to the lodge on a cold morning, getting a (free) cup of good coffee in the lobby and sitting on the porch in a rocking chair watching the sun rise above the rim.
One highlight is taking the Pinnacles Road out to see the volcanic spires. If you want to take a boat out to the biggest island in the lake, you have to hike about a mile down from the rim to the dock. I prefer hiking the trails up to the rim high points.