It can be as long or as short as you want it to be. It is self guided they just give you some information when you arrive at the castle and then you are free to explore as you like. They also give you the option to walk up to the castle or they provide a free shuttle bus.
It's a self guided tour besides a quick bit of information they sit you down for before you go in. You can take the free shuttle bus to and from the grounds, or you can walk there and back. I have gone a few times and it's been worth the trip each time. There are also waterfalls and lookouts on your drive up, so be sure to budget in some time to check those out.
Make sure to save an hour for walking up or down the creek
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