The science picture section on telegraph.co.uk has some fun stereoscopic space images like the one above.  Stereoscopic imaging creates the illusion of depth from 2D images.  You can view them by place the image in center of the screen and, sitting at a normal distance, slowly crossing your eyes.  Continue doing so until the two images overlap, creating a “third” image in between.  Then adjust your focus on the middle image, keeping the two overlapped.  Ta da!  It might take some practice, and some images are easier than others.  Head over to telegraph.co.uk and give them a try.