At the Summer Camp in the Rockies, we have two outside weapons sessions every day. The last couple of years it was held in the soccer field which had a great view of Mount Sopris (to which we bowed as the "shomen"). I believe this year we're going to have a big tent near the dormitories so we don't have to walk too far.
At Saito sensei's seminar last year in Denver, we had a weapons session outdoors on Sunday.
I've also been a part of a demonstration which was held outside with mats on the ground. I would have liked to have worked out with some of the judo folks but I didn't get a chance...