The paths themselves are wonderful. In nearly all cases, they are based on the original inter settlement routes and are as old as the villages themselves. Designed for pack horses/ponies as well as pack people they are perfectly graded and walking along them is a real pleasure.
Depending on how much time you spend in the churches (they are not that big) you can get around the valley in 9/10 hours. It's a challenge, but not quite as mad as it sounds as the paths are so easy and such a pleasure stopping is a problem.
I went round in a day, a wet day at that, and thoroughly enjoyed it. In describing the route I will try and point out the options a more sensible person would have considered, but there are definitely two good circular walks.
Staying at Boí, at the northern end of the valley, I was able to pop into the National Park information centre and get some helpful advice on the route as well as a map. The churches don't open until ten and how many of them are open varies according to time of year (not that many in October)
Book recommendations for this region: