This is Bodiam Castle – when I grew out of children’s parties (for which my Mum sewed me long party dresses – how times have changed!), I always chose a trip to Bodiam.
The castle was built (or rather a house extended and fortified) to repel pirate raids. As the sea has receded it’s hard to imagine that this was in dangerous territory – although the WW2 tank trap is a reminder that invasion was feared not that long ago (although with a sodding big castle, why do you need a tank trap?).
[The Boy tells me that this is because a tank would “Blow the shit out of the castle”.]