I attended this two years ago, when the headline show was A Midsummer Night's Dream, a play I can watch over and over and over again and never get bored of it. It was staged in Trinity's Rose Garden, which is a gorgeous place at the best of times, and the open-air performance of this wonderful fairy tale made it absolutely magical - rain and all! The seating was built by the wall of the Museum Building, and the action took place amidst the natural trees and bushes on the other side of the path. The sight of Titania's fairies peeking from behind real trees was delightful. I found that the arrangement made the actors sometimes hard to hear, and as it began to rain, it did get rather cold to sit in the wet evening, but fortunately (and generously) free coffee was served during the interval to warm the audience up. I can only imagine how cold the actors, especially the ones in the skimpier clothing, must have been. Nonetheless, the sense of magic was further enhanced by lights in the garden as the evening grew properly dark. I think just the fact that I can still remember this event very well illustrates how well it was done.
I very much recommend going to see the events of this festival. The DU players blog post to which I linked above promises more details and a website coming soon, so I will be watching that space.