From the proposed sites I have only visited Glendalough (May 2017). As Nan has already pointed out, it is a fairly easy day-trip from Dublin, although we chose to stay at the only hotel next to the ruins. This proved to be a good choice as you can enjoy the site early in the morning or in the late after noon. The monastery was probably big for its time, but visiting it today will not take you longer than an hour. There is a modern visitor centre worth visiting and there is the obligatory hike from the monastery to the upper lake, where ruins from the same age can be viewed. These belonged to the monastery and served monks seeking solitude in the woods. The natural setting is very pretty. The site, including the hike, are very popular and although we did not visit it during high season there were a lot of visitors around, including many school groups.