Spirals are a great way to visualize an endless repeating of something. Stock image sites are full of images of real staircases, rendered ones, or other images that have a spiral structure. You can use the visual as-is, or add text (maybe in circles that get smaller and smaller) to shows that something is going on forever, that something is repeatable.
Some people associate a diagram like this with a downward spiral. I do not see it that way, you?