Bass Lake in Point Reyes National Seashore has everything you would want in a perfect summer day: hiking, a rope swing into a lake, picnicking, and gorgeous views.
Follow the Coast Trail from Palomarin Trailhead to Bass Lake. It's a fairly easy ~2.5-3 miles to the Lake. As soon as you pass the lake, on the left you will see a narrow unmarked dirt trail. Take this trail and you'll get to a nice clearing with easy lake access (this will be a great spot for lunch in the sun after swimming). To continue to the rope swing (which is a MUST DO), follow any of the narrow trails at the other end of the clearing. You'll soon arrive at the small steep clearing from where you'll be re-living your childhood by swinging into the lake! Don't forget to bring your swimming gear, inflatable rings to hang out in the middle of the lake, and a pack lunch! (Note: there's poison oak along the narrow trails, so you might want to avoid shorts or flip-flops.)
After enjoying the afternoon by the lake, take the same trail back and drive to your already secured camp site on Mount Tam. Feel free to stop by the town of Bolinas or Stinson Beach for a drink at the local pub before heading back to camp. You can even add a hike to Alamere Falls from Bass Lake for additional adventure (but beware of the massive crowds at this location on the weekends).
Here is a helpful Trail Map from the NPS. Dogs are not permitted.
