Wichita Mountains NWR, OK
Last weekend, Tarp and I met at the refuge for a bit of recon and hanging. I'm not going to post pictures, but will include a link that discusses the area in depth, and includes some excellent pictures.
Backpacking overnight in the back country is by reservation only...we, of course, failed to plan ahead, and so ended up in the only developed campground with about 5 million people on spring break. It was not as bad as it sounds, and was actually pretty comfortable, with plenty of trees for hanging. There are two group camps with shelters that would be excellent for group hangs.
By contrast, the back country is short on suitable trees, but has plenty of trails and off-trail opportunities, including rock climbing. There are numerous lakes in the area, both on and off the refuge, so fishers and kayakers have plenty of options. It's worth a visit.