We took the first ferry over in the morning and planned to return mid-afternoon. We should have packed a lunch and planned to spend more time. We rented bicycles and did the 5 mile perimeter loop. I hadn't ridden in many years and I found it difficult to deal with the hilliness of the route. My husband, who is an experienced cyclist agreed with me that my bike's gears weren't shifting properly so that might have been part of the problem. We were also told that the route was "relatively flat" with a couple of hills. We read that it was a beginner trail. Not true, as far as I was concerned. The views were truly beautiful but we didn't stop much to admire them. We did see many deer along the way and there were sea lions on the docks when we first arrived.
Apparently there are some lovely campsites on the island. Three mothers were on the ferry with their small children. It sounded like a very fun thing to do. While there was no fee for the park, there is a fee for the ferry and the bicycle rental was $12.50 per hour.