Race Against Time
Time to move, Commander. Open the galaxy map to find a new cluster available to you: the Pangaea Expanse, which is marked with an "Ilos" label.
Select that cluster, then choose the Refuge System as your destination. After making the FTL jump, highlight planet Ilos and press the left mouse button to travel there.
With stealth systems engaged, Joker dips the Normandy down through Ilos’s atmosphere, making a near-impossible Mako deployment amid a clutter of crumbling ruins. Watching in disbelief, Saren rallies his forces into a nearby bunker and seals a massive security door behind them.
No amount of brute force will open the door, and your heroic crew is forced to explore the nearby ruins to find another means of entering.
Ilos: Upper Ruins
Geth forces are inbound, so waste no time piling your squad into the Mako. Turn the vehicle’s cannon on the geth troopers heading your way to annihilate them in short order.
Hunks of debris prevent the Mako from traveling very far into the ruins, but drive as far as possible and use the Mako’s superior weaponry to eliminate as many geth as you can.
Proceed into the ruins on foot, moving between various bits of debris to avoid being picked off by the geth soldiers stationed in the plaza ahead. Fire on the geth from range, working at securing the vicinity before you advance.
Terrible Twosome
Move forward with caution: a pair of geth armatures stands in the narrow passage just south of the plaza.
Take cover behind one of the large rectangular stones at the plaza’s north end and fire at the armatures from around the corner, just as you did during the stalker/armature ambush back at Therum.
Remember to dodge the armature’s deadly pulse blasts at all costs; these projectiles are lethal against ground forces.
Lower Ruins
If you’d rather not fight the armatures, dash to the side passage west of them and descend the steps that follow.
This takes you to the lower ruins, where you encounter heavy resistance in the form of geth soldiers and hoppers, and even a few assault drones near the southern end.
The lower ruins provide a means for you to circumvent the armatures. Simply cut your way through the weaker geth forces here and return to the upper ruins via the southern staircase.
In addition, if any member of your team has a high score in the Decryption Talent, you can decrypt the armature controls in the lower ruins to deactivate the mechanical goliaths in the ruins above.
Upper Ruins: Courtyard Assault
South of the plaza is a small courtyard area that’s crawling with geth. Tip the odds in your team’s favor by exploiting a fantastic sniper perch that’s just northwest of the courtyard.
To reach this spot, simply follow the trail south from the plaza. Run up the short, weed-covered slope near the low wall while crouching to press Shepard’s back against the wall.
The courtyard features numerous troopers and a formidable destroyer. Open fire from the northwest perch, holding this position until you’ve wiped them all out.
Stop firing and take cover whenever the destroyer launches a Carnage blast at you. Clear the courtyard, then scale the weed-covered slope to advance.
Heads up: a pair of shock troopers opens fire from a remote southeast balcony the moment your squad moves into the courtyard.
Sprint eastward and take cover next to a tall stone pillar. Peek around the side and fire on the shock troopers to drop them both from range.
Return to the courtyard after eliminating the shock troopers. Find and open a crate near the western wall, then move uphill, pressing Shepard’s back against the low southern wall.
A hoard of hoppers leap about the courtyard’s elevated southern half, and this low wall provides ideal cover as you work at eliminating them.