An oldy but a goody where's Waldo (wally) is sure to please. While the physical books are probably a no go you can count on Google to come to the rescue. Sites like this make it easy! You can challenge yourself with a timer, challenge others and if you're really about to lose the plot you can bail out and hit "give up", Wally will magically appear!
Handy hint, dim down the brightness on your phone so you don't fry your eyes.