We were told it was a short hike from the Glendalough Hotel to the Upper Lake. It is, if you know the way! We got up very early with a goal of being at the lake's edge for blue hour and then sunrise. It was worth getting up early.
As it turns out, the proper trail back to our hotel leads right through the monastery, the other site we wanted to photograph. Not only that, but when we were told we would be close to the best photo opportunities we did not expect to see the entrance to the park and the monastery right from our hotel window!! We had simply taken the long route to the Upper Lake in the dark, walking right past the entrance!