Something that's really very simple, but looks modern and intricate.
Just remembered doing something like this when I was a kid and thought I'd show it.
I don't remember what it was called exactly, but it reminds me of a puzzle.
First off, you need to make your template.
Find a sort of thick paper, like cardstock. I used an index card.
I don't recommend using cardboard, as it might be hard to cut out evenly and use for this, but you can try it if you want to.
Now cut it into an even square.
It doesn't matter how big it is, but just remember that the smaller it is, the more work you'll have to do.
Mine was around 2.5 inches, or about 7cm.
Next, draw a sort of wavy design on one side of your card.
It's important that the line touches both corners of its edge and doesn't stretch out into the middle.
I don't recommend doing something very intricate, and simple things look nicer with this project anyway.
Next, draw another line on a different side that is NOT opposite the one you just drew.
When you're done drawing both lines, there should be an empty side opposite both of them.
Pick a color and color in a random piece.
Now follow this example and color it in sort of like a checkerboard.
No two same color sides should touch, but the corners will.
I recommend using a neutral color and a bright color or pattern, because it might be a bit too loud if it's 2 bright colors.
I always use white and another color.
Now you're done with your new work of art.