The castle is good trip out,don't know the opening hours but probably shut for the usual times.They have those walkie talkie type things that tell you all about it.
The Barca or ferry is about 5 minutes the other side of Benifallet (sign posted Pas de Barca on the left ) and is shut the usual times,about €3.00 per car,weather and river permitting,there will be a red pair of underpants flapping in the breeze if it's not working and if you've never done it before and you're first on, may I suggest a possible change of underware.