(See the Iapetus Gallery)
Iapetus is tide locked so it always shows the same side toward saturn. It runs into debris as it travels around Saturn. As a result the leading side of Iapetus is covered in dark debris and the trailing side is white as snow giving it a cookies and cream look. The leading side is so dark that Cassini said he could only see Iapetus on one side of Saturn, but not the other.
Iapetus is composed mostly of water ice which is implied by it's density of 1.1. Cassini revealed a ridge 13 kilometers high at least 1300 km long and parallel with Iapetus's equator. The orbit of Iapetus is inclined by about 15 degrees to Saturn's main orbital plane. See more of Iapetus.