Could someone do that in the D&D universe? Not necessarily create entire environments, but maybe a person or two to interact with. I have a very lonely sorceress in my campaign, and, well, she was wondering if she could use an illusion for more than just fooling the baddies. (Yeah, she could go get a boyfriend, but this is more fun. :D) How powerful a spell would she need to use? Would Major Image suffice, or would you want to use a persistent image or programmed image? Obviously, if this is something for amusement's sake, lower level is better.