£28 to visit the castle/gardens, and £3 for the boat.
I've always wanted to visit here, and glad that I finally have.
I think it is overrated.
The parking situation is a nightmare.
The walk over the causeway was the only fun/interesting part.
The walk upto the castle wasn't particularly challenging or difficult as I am able bodied, but several people did seem to find it challenging on such a hot day.
Anyone with mobility or health issues will need to reassess visiting, as there are no wheelchair routes/ramps and the ground in several places is loose/cobble/rocky, with large steps and often you have to scramble up parts of the path.
The shops are staggeringly overpriced, and we avoided buying anything from them.
The garden was predominantly a large selection of succulents and palms with nothing of interest.
The castle, wasn't particularly interesting with only a small potion of it accessible. The "gallery" they have on the way out had some interesting pictures/paintings but no information to give context to them.
You can quite easily walk around the garden and castle within an hour.
As others have mentioned, the causeway is tidal so make sure you are aware of the times as several people did get caught out while we were there.