This moon has a bright side - the side we can see from Earth - and a dark side, with a dramatic transition zone between them. I've arranged the photos below to emphasize that light-to-dark nature. This is also the world with that massive wall going around it like the ridge of a walnut. To see more of that feature, check out my previous AIotD here.
Without further ado, Iapetus:
Click the images to see the NASA story and get high-res images.