Ideas for corporate team building - outdoors?

It will be for about 20 people who are all pretty picky. We have been trying to think of things for a while now, but have run into a brick wall. It will be our summer outing, so preferably something outdoors would be good. Also, not too physically strenuous. So far, we have thought about rafting (on a beginner's course), an outdoor picnic with team building games, or a scavenger hunt. There seems to be quite a few objections to all options. Any help would be greatly appreciated. Thank you!