Both castles owe their initial fortifications to William, Lord Hastings, a favourite of Edward IV (just like one of the ancestors of my fictional aristocrats).
The castle is most impressive, even in its present-day state:
The grounds also contain the ruins of two sixteenth century garden towers, and the impressions of the sunken gardens are very obvious as you walk across:
It's possible to see the room layout of the great tower from outside, and also to climb it:
Then there are the kitchens:
The great hall:
And underground tunnels:
I can highly recommend the audio tour too. Full set of photos starts here.