OK - cost a little expensive but FREE in you're a member of the NT. Do NOT attempt the causeway walk or the climb in flip-flops. Foot-ware priority: strong boots, well-fitting trainers (Americans call them tennis shoes). I was in trainers and was ok but boots would have had the edge. The causeway and many of the paths are cobbled. You can take a boat tide permitting - don't know the cost so plan your trip according to the tide timetable (Google it or on display at the harbour) as at high tide the causeway is impassable. Really surprised at the history and the decor. It was so interesting with helpful and friendly staff at sentry only too eager to explain, so do ask. Take a camera and explore the garden too. You can purchase a castle ticket, a garden ticket or one combined. It is a hike up with rest stations but even those with a walking stick managed it. Give yourself 3 hours to really appreciate the island and to take in the views. Binoculars might prove useful. Picnics are accommodated in several areas, one of which is within a kiddies' play area but there is a cafe and a National Trust restaurant for those travelling light. Car park: there's a Council version by the old station for those with a weekly Cornwall pass (Google in advance of your holiday if you want one). If you need to pay to park I suggest you get a berth in a private car-park as near as possible as you'll be exercising your legs enough on the climbs. Shop has local produce (rhubarb wine) and ice-cream is available for those of us who never grow up.