Titan is Saturn's largest moon.
It is larger than Mercury and has a planet-like atmosphere more dense than those of Earth.

The interplanetary voyage of Cassini / Huygens took seven years, and made use of successive gravity boosts from Venus, the Earth and Jupiter.

Huygens descent towards Titan lasted nearly three weeks after the separation from the Cassini mother-craft. Following aerodynamic braking in the upper atmosphere, then deployment of three parachutes to control the descent, the probe landed on the surface of Titan.

Artists Concept:
Huygens probe at Titan

The Orbiter Cassini is in orbit around Saturn for its own observation mission, while relaying data from Huygens back to Earth.