What makes Titan so special among moons?

The answer

Saturn's largest moon Titan is the only moon in the solar system with a dense atmosphere (1.5 times Earth's surface pressure) and the only place besides Earth with stable liquid on its surface. However, Titan's rivers, lakes, and seas are filled with liquid methane and ethane at −179°C. Its atmosphere is mostly nitrogen, with methane playing the role that water plays in Earth's hydrological cycle - evaporating, forming clouds, and raining down. Beneath the surface, Titan may also harbor a subsurface water ocean, making it a candidate for two completely different types of potential life.