All along the streets of Carlingford you'll see various medieval buildings right in between the houses and shops.
This is for instance the Carlingford Priory and is actually in a rather bad state of repair in comparison with places like the Mint or the Jail. It's still quite something and I enjoyed walking around there very much.
I haven't managed to find out what the relationship between this castle and King John's Castle in Limerick is. I can only assume that it would've been the same King John who commisioned both but what he would've come to the west of Ireland for is a mystery to me.
The castle is rather cool and the way they light it up at night makes for a great landmark.