One of my favorite moons in the solar system has to be Hyperion. This small icy body is one of those truly weird places.
An oblong shape roughly 360 x 200km (220 x 120miles) the moon is composed of primarily water ice with a small amount of rock in the mix. The moon is thought to be highly porous, a loosely held together rubble pile perhaps. This is indicated by the odd appearance of the many impact craters, looking as if the impacting body is absorbed as much as vaporized. The material of the crater walls then slumping back into the void.