Probably much better to visit during the summer, but we were there in February. The upside is that they don't charge an entrance fee in February. It was quite a work out, but I enjoyed it. We had some spectacular views, but since it was winter, the scenery wasn't as green as we would expect. There were no flowers in bloom and only saw one flock of sheep and no horses. But I still enjoyed it just for the views alone! You can climb to the top of the mountain and look out over the terrain and see for miles. Words could never describe the beauty - even in winter.

It is indeed better to visit it in the summertime, more people around as well though, especially in the weekend. Lovely little museum with a short history of the area and the landscape, some explanation of the plants and animals that can be found. If you can spare a few euros you can buy little booklets with explanation of the trails. There are several, the shortest one is through the forest and takes only half an hour or an hour. There are others going to the top of one the mountains (or is it big hill?). Relaxing and beautiful.

The Connemara National Park is a beautiful place for a ramble whatever your level of fitness. The visitors' centre has a nice cafe and brilliant museum on the ancient and recent history of the area as well as the importance of wetland ecosystems.
Diamond Hill is well worth the climb but the woodland walk is gorgeous April-September.