I created these hand-drawn stereograms at around age 12. They are not the greatest works of art, but are a fun peek into my nerdy past.

To view, relax your eyes as if you're looking through your screen at something much further away. Stare until four images appear. Then allow the images to converge to a set of three, focusing on the center image. Here a three-dimensional space will emerge. If the display on your screen is too large, most browsers will allow you to zoom out with ctrl-minus or option-command-minus. Return to normal with ctrl-plus etcetera. More info about stereoscopy via Wikipedia.