That's actually a super easy project that doesn't really require any artistic talent. Unlike some of my other favorite whimsy projects (e.g. ball-in-a-ball, chains, etc.) it involves removing very little wood, assuming you have a cube of appropriate wood to start with (something easy to carve with even grain like basswood or yellow cedar is a good place to start). You just carve a roundish shape like this into each of the six sides:
It doesn't require removing that much wood at all before you'll break through to the other side around the bars of the box, and you just keep going until all the sides are free. I like it as a starter project for people because it doesn't take forever to finish.