First, get a few solid fruits, things like apples, pears, maybe even bananas. Just not something that’s mostly water and pulp.
Next, take a nice sharp knife and cut out rectangular bricks from your fruits. The bricks should be of a uniform size.
Now, mix up your fruit-bricks so the colors and textures are randomized. Take the bricks and build a castle with them.
Maybe your castle will look something like the one’s Mr. Escher draws. Be careful how you make the stairs overlap.