We spent the day in Conwy exploring the walled town. We visited Aberconwy house which is a National Trust property and is the only example of a Medieval merchants house left in Conwy.
A visit to the castle is well worth it, and there's plenty to explore. Apparently they sometimes have plays in the grounds. When we visited there were demonstrations of archery, and the chance for the kids to dress up in armour and learn the finer points of sword fighting. Conwy also has its own resident jester who was at the castle performing when we visited. During the performance I was singled out to take part as a coerced volunteer and asked to lay on the floor so the jester could juggle knives and walk over me. It probably looked scarier than it was, and it was all in good fun.
In all Conwy is a good day out for the kids, but it can get busy when the weather is nice. If you decide to stop for a chippy tea in the harbour after a long day of walking, and maybe even a pint at the Liverpool Arms, just watch out for those cheeky seagulls.