that would be awesome. jump in slide around the bottom side and shoot out. it would have to be really big horizontally if you want it to be 6ft deep. and if you got stuck in it you'd be done.
there was a make shift vine rope swing at the enterence to the kiddy park it was pretty fun. but id say a cool line of 2 or 3 different rails( C rail/box to down rail)
Mabeye like a huge hallow tube, like 15ft tall, with HDPE on all the surfaces. You could hit either as a huge rail type type, or you could go inside it and slide around. Would be really expensive, but so cool.