Illium is a wealthy Asari world with few laws and regulations. It is infamous for its nonexistent worker protection laws, but due to its safety and excellent infrastructure, as well as its beautiful views, it is a major tourist destination.
On Illium, Shepard meets his old companion Dr Liara T'Soni, who directs him towards two squadmates, Samara and Thane Krios. Miranda's loyalty mission takes place on Illium, and there are several optional side quests available, including two for Liara herself.
