Hint 1! If you managed to establish a love affair with one of your companions, this will be the time to have a little tete-a-tete with him/her.
Hint 2! On Ilos you will be fighting mostly with geths so it's good to equip your squad in weapons and upgrades against synthetic creatures.
11.1. Into the ruins
LEGEND (Map IL1):
A. Archive Door
B. To the Lower Ruins -> (IL2-A)
C. To the Security Station -> (IL3-B)
D. To the Lower Ruins -> (IL2-B)
E. To the Security Station -> (IL3-A)
LEGEND (Map IL2):
1. Armature Control
A. To the Upper Ruins -> (IL1-B)
B. To the Upper Ruins -> (IL1-D)
LEGEND (Map IL3):
1. Security Panel
2. Armature Repair Station
3. Armature Repair Station
4. Armature Repair Station
5. Armature Repair Station
A. To the Upper Ruins -> (IL1-E)
B. To the Upper Ruins -> (IL1-C)
After landing and chasing Saren for a while, you'll be forced to stop and find some way to get inside - he will block the door leading into the ruins (IL1-A).
Stay in Mako and use it to clear the area. Then leave it and continuing slowly from cover to cover eliminating geths in front of you.
Soon two armatures will stand in your way. You may try to destroy them hiding behind a cover, using overload and sabotage, shooting and avoiding big electronic shots.
Easier way is to use nearby passageway (IL1-B) to the lower level. Here you will have to fight as well, but with regular geths only.
Hint! You can use console (IL2-1) found along the way to deactivate armatures on the higher level. You'll need to have someone with high decrypting skills.
Use the south passageway (IL2-B) to return to the higher level. This way you can evade the armatures.
There will be open terrain in front of you with more geths. Avoid exit from the north. It's better to take cover using way along the wall. There will be snipers shooting from above (balcony on the southeast side of the room), co be careful. You can use pillars as a cover.
Use the elevator (IL1-E) to get to the security station. At the end of it, there will be door to security panel - your destination (IL3-1). Before you'll get there, you'll need to fight with enemies, including geth prime. Concentrate on it first.
Then (optionally) continue further using consoles to reprogram and activate armatures (IL3-2,3,4,5) which will give you good support.
It's also good to force your way to the north and get up the security building. You'll have good view to the whole room and the walls will be good cover.
After the fight use the panel (IL3-1) to open door blocked by Saren and hear some message in prothean language. You won't be able to get a lot out of it though.
Take the elevator (IL3-B) on the north to get near Mako. Ride further.
Continue along the corridor. There will be some geths there, but eliminating them shouldn't be difficult for you.
Soon you'll reach big energy barrier blocking further way. Leave Mako and go through nearby door. Continue along the corridor and take the elevator up. It will take to a room with prothean terminal. Use to contact Vigil, ancient VI controlling complex on Ilos. During long conversation you'll learn a lot about history of protheans, reapers, Canal and Citadel.
After the conversation, VI will give you a copy of a special data file that must be uploaded into the Citadel's master control unit to give you control of the station.
Return to Mako. The barrier will be gone, so continue further. You'll encounter some geths along the way, so be careful, watch the radar and eliminate them from the distance. Soon you'll reach the beacon.
Passage will be open and you'll have 30 seconds to get there. There will be several colossi along the way, but you won't have time to fight them. Just ride and don't bother with vehicle damage - it won't be necessary soon.