If you want a campground that has amazing hikes within a few miles and that's feet away from a majestic lake, then you are in the right spot!
The campground is right at the very north end of Lake Crescent. It has bathroom and potable water, and for just $20 a night I think it is well worth it. Each campsite is equipped with a table and firepit (bring firewood). Open between May and October; first come first serve.
As for activities, the list is endless. You can kayak, paddleboard, swim, dive, really whatever you feel like. The lake is beautiful. On a really clear day you can see down at least 75 feet. There are tons of hikes around too. The hike we did during our stay was Mt. Storm King (Trailhead about 7 miles away). Brutal hike, but once you've enjoyed the lake it's nice to really get a sense of how little you are in it. Mt. Storm King gives you those views.
When you need an easy place to set up camp and not to far from Seattle, this really is a wonderful place to distance yourself from technology and the "hustle and bustle" of the city noise.