Is it possible to walk to the fort from rattlesnake Island? I saw on Google maps a parking lot and there's a large land connecting to the fort. Is this private property or open to the public?

No visitors unless guide is present

It's a park open to the public. It's FREE. The ferry and visit of the Fort all free. At the park you can walk thru a trail that's ends on a beautiful view before taking the ferry to see the Fort. All visit is guide at all the time. You will stay like 40 minutes total ferry and visit. It's is small place and they take only 15/20 visitors at the time. Recommend to go early for the tickets to embark. It's all free and the history of the place explained very clear..very interesting ..the park has a parking lot, bathrooms, trail and ferry. You can also visit across the park the beach, beautiful area and a walk distance. We have a great time and learn a lot about St Augustine. Enjoy your trip!