We will be in Ireland Nov 18-Dec 5 and want to visit both Glendalough and Conmacnoise but don't know if we can do that much driving. If you had to choose which would you do and why? Thanks.

I'm not sure if you mean to be doing these both on the same day? and if so, where are you starting from? I would think the days will be very short at that time of year - also a factor if you're trying to do both.
Regardless: I can only tell you that we visited Glendalough very early September '08 on a day of pretty much "downpour" weather - the tour of the small chapel area was pretty brief, but interesting. But, walking around the lake, and even driving around part of it, was really not interesting. It was our only day that we weren't thrilled during the two weeks. My favorite part was probably learning the history of St. Kevin, in truth (have a brother of that name). Didn't get to Clonmacnoise but it looks perhaps larger? Therefore might be more interesting?
I have the feeling I haven't helped....good luck choosing! If you do choose Glendalough, there's a very visible little restaurant that we ate at (you can't miss is, really) and we had a surprisingly good lunch there on our blustery, cold day.

I'm not really qualified to answer this because, as much as I'd like to go, I've never been to Clonmacnoise. But I just wanted to say that our experience of Glendalough was much different than jo_ann's. We enjoyed it very much when we were there this past June. While not cold and blustery, neither was it a terribly nice day. But we found Glendalough to be a beautiful spot. And the drive there through the Wicklow Mountains was very scenic.

Frankly, I'd be very tempted to try to do both. And that should be doable in a two week trip. But, of course, it depends on what else you're planning to see.

Like CAPH52 we've only visited Glendalough -- it was a summer Sunday and so was very crowded...nothing like the solitude St. Kevin sought! Am sorry we missed Clonmacnoise -- it doesn't have the natural beauty of the Wicklow Mountains, but the settlement seems impressive...

You will need more time to visit Glendalough IF you do not plan just to see the main site, but also want to have a walk in area, or plan to explore the Wicklow mountains by car.
Clonmacnoise is a rather compact site by size, easy to reach when going from Dublin to Galway or vice versa.
I don't know if I wanted to "do" both in one day.
If you feel the need for a 2nd destination after Glendalough, I'd think about nearby Powerscourt house and gardens.

I was in Clonmacnoise in June of this year, the weather was fantastic and made the day quite enjoyable. It is a compact site and wouldn't take long to walk around it, that said you could easily spend a couple of hours if you were in no rush and enjoy the relaxing atmosphere.
There is a twenty minute video in the visitors centre that goes through the history of the site. You can also get a guided tour (30 minutes) I didn't get one but i think you would get a lot more out of it if you did do the tour.

I've been to both on glorious days. I loved them both, but for different reasons.

Glendalough is absolutely beautiful. We went in late May; the drive was gorgeous with all the grouse in bloom. The site itself is impressive with the round tower, celtic crosses, etc., but there are also hikes you can do to see natural scenery. The Wicklow mountains themsevles have a lot of history.

Clonmacnoise is more compact, in that there is no hiking in area. I would guess it has more crosses and they are of more significance. It also has a round tower and church/castle ruins. Its on the river Shannon and has a beauty all its own.

I suppose your choice depends on the other parts of your trip and your interests. You can't go wrong with either one, although my preference would be Glendalough.

Reilly, not to be snarky, but it is gorse in bloom. (Grouse are birds sort of like pheasants, a bit smaller perhaps).

Both are wonderful places. I have been to Glendalough many times as I lived in County Wicklow for a couple of years back in the sixties. Except for one visit, it was misty and/or drizzly when I was there, which sort of added to the atmosphere of the place. At the time of year you will be visiting, it will not be so crowded as in summer. The first time I went, there was no visitor center. We just parked near the lake, and had to eat our pcnic in the car as the wild donkeys were very interested in our food. I have a picture of one trying to stick his whole head in through a half opened VW window. In later years, I have found the visitor center very interesting with an informative video about the history and geology of the region. Returning to Dublin through the Wicklow hills is a great drive--seemingly empty miles, some waterfalls, and even in November some somber colors.

Clonmacnoise is also interesting. The first time I saw it, it was sort of deserted and things were just there for you to walk around. Now there is a visitor center and the most ancient of the crosses are inside in glass enclosures to protect against further weathering. Replicas have been placed outside so you can get a feel for what it was like.

If you are considering driving to either site as a day trip from Dublin, I would do Glendalough. It would be a push at that time of year to drive to Clonmacnoise and back in daylight. However, if you are doing a trip to Galway for an overnight, Clonmacnoise would make a stop on the way.

Glendalough is my favourite place in the whole of Ireland. The hiking is wonderful and not too difficult. I would recommend walking around the Upper Lake so that you get great views of the valley. And also walk around the Monastic City at night. Magical! I have some pictures if you're interested.
http://www.jeremytaylor.eu/glendalough_ireland.htm