Titan: the only moon to have clouds and a dense atmosphere

Mosaic of Titan from Cassini's February 2005 flyby. The large dark region is Shangri-la.

Titan referred to as the biggest moon of Saturn in the solar system. Titan was discovered telescopically in 1655 by Christian Huygens a Dutch astronomer. This moon was named for the titans of Greek mythology (which meant the children of Uranus and Gaea and their descendants). This moon is known in the solar system as the only natural satellite to have cloud and a dense atmosphere. 

Amazingly the titan is bigger than planet mercury and, in significant ways; it resembles a planet than a typical moon. No trace of Oxygen on the satellite, but clear evidence of stable bodies of surface liquid has been found. There is a large amount of nitrogen in its atmosphere; methane and ethane clouds and nitrogen-rich organic smog. Climate which includes wind and rain creates surface features similar to those of Earth: surface features include dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas. Its rotation period is synchronous.