Fun stuff.. tricky for me.. what you're supposed to see is a 3-d object floating on a flat background.. but at first what I saw was the background in the foreground and a 3d-hollow cut out of depth inwards, which didn't make much sense to me.. I am able to get the full effect if I take my glasses off.. but I am also able to see multiple layers of depth as well if I look at it differently.
Some images are easier to see than others.