Are you at all a pinball or classic arcade fan?
The
Las Vegas Pinball Museum is worth a look if you are. There are dozens of pinball machines, spanning every decade, and also some classic arcade games like Battlezone, Crazy Climber, and Track and Field.
Great for nostalgia and wagering against friends. It is not far off the Strip, only a $20 cab ride or so, but better if you have a rental car (because you will have to call a cab company and wait for return pickup).
Also, consider using the spa at you hotel and getting a massage. It's a great way to relax, break up your day, and feel pampered.