The backcountry campsites at Castle Rock State Park are an easy 2.5-mile hike from the main parking lot. You can take the Saratoga Gap or Ridge Trail to get there, as this campground is at the apex of the loop.
The campsites are well maintained, spacious, and come equipped with fire pits and picnic tables. Finding level ground should not be an issue here. Potable water is located in a few locations throughout the campgrounds. A small amphitheater, restrooms, and a bad weather shelter is provided as well.
The only real downside to to this otherwise fantastic campsite is the constant gunfire from a nearby gun range. Despite that fact, this may be a good spot to launch onto the Skyline to Sea Trail. The first 2.5 miles of the 30-mile trek to Waddell Beach is at this point.