Ilos is a former Prothean world which has been uninhabited for millenia. It can only be reached through the Mu Relay, and therefore has never been investigated.
Shepard discovers that Ilos is the location of the Conduit, a miniature Mass Relay that allows transportation to the Citadel. Here, the team finds a Prothean Virtual Intelligence named Vigil, who gives them information about Saren Arterius and the Reapers. The team drives into the Conduit and is transported to the Citadel for the final battle.
