I often feel a little sorry for tourists, especially the ones that sign up for whistle-stop tours around the highlights of a country or a city - they see the famous beautiful places surrounded by other tourists instead of locals, and remain insulated from the true culture of the place they are visiting. In many cases they don't speak the language.
Three Castles Head on Mizen is not one of the very famous places in Ireland. I had never heard of it until 24 hours until I visited it. You go down to the end of Mizen Head - not the lighthouse complex perched on the cliff, the other end - and you leave the narrowish road that can just about handle two-way vehicular traffic (with care) and go onto a genuine narrow and twisty country road, that goes up and down in the rocky landscape. Personally I would think twice about going down one of these in any vehicle larger than a medium-sized car, and I would ixnay a camper van absolutely. And taking a coach down here is out of the question. You get to the car park, and go through the field beyond to beside the farmhouse - which has a very good café, I've been told - and put your three Euro per person into the box, and follow the well-worn path through the fields and up and over the hill. The path veers right, it's kind of rocky, but beautiful, and a few minutes later you see part of the lake, and then you go around a smallish hill, and you see the remains of the castle keep. Three towers still stand, hence the name Three Castles, and the structure is sheltered from the worst of the wind and sea spray by being located in a dip below the cliff edge. The lake you've already seen extends from the base of the castle wall right down the valley to the very edge and is held in by a pile of rocks - it's believed to be artificial, and built around the same time as the castle, the mid 1300s.
It's a beautiful valley, and hidden, and you need to allow a good 20-30 minutes to get there from the car park, but when you get there, it's 'wow'! We sat out of the wind, took photos, and enjoyed the wonder on each other's faces. I think it would be a nice walk for parents with active youngish children, and I don't imagine it would be an issue if you wanted to bring your dog, but he'd have to stay on the leash - this is a sheep farm, first and foremost.