Is there a good alternative to the "deck" for outdoor activities? 

Yes, there is another way of being outdoors that is not met by a deck - the outdoor room. An outdoor room is a partly enclosed space, outdoors, but enough like a room so that people behave there as they do in rooms, but with the added beauties of the sun, wind, smells, and outdoor sounds. This room needs to be defined at its corners and possibly partially roofed with a trellis, for example. "Walls" around it could be created with fences, sitting walls, screens, hedges, or the exterior walls of the house itself.

Dr. Ronn Phillips, Arch.D., and Bobbi Hauptmann
Environmental Design, College of Human Environmental Sciences, University of Missouri-Columbia