Well I live in Northern Ireland and there are lots of castles, Carrickfergus being the main one. If you are interested in castles in Northern Ireland reply to this post and I will let you know of the locations, visit times and days open etc.
If by fully working, tourist friendly castles there a few across the country, nearly every county has one.
But the majority are broken down, ancient ruins and they are dotted all over the place.