Roscommon castle, just today. Although we didn't really visit there castle as such, we went for a walk in the park that surrounds it. It's just around the corner from where my husband grew up and where his parents still live.
The thing about living in Ireland is that there's ruins everywhere; castles, but also abbeys, and even older stuff such as ring forts. Even in Dublin, where our home is, there's old stuff dotted around the suburbs.
Because you can't go anywhere without tripping over an old castle, I do think we probably don't appreciate the heritage around us quite as much as we should.