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Jump up the right ledge to reach the top.
Go up the stairs.
Walk through the observation corridor.
The path will be a dead end. When you go back you will be attacked by aliens.
Jump through the broken window.
A big alien will teleport and block your way. It can fire bolts of electricity in a straight line but you can dodge them by side stepping. If you don't want to fight it you can just lure it away and then enter the passage in the rocks.
Use the lift to go up.
Go towards the elevator on the right.
Jump through the door on the right to go inside.
Climb to the elevator hatch.
Go up the ladder.
Jump at the fallen door.
Reach the end of the corridor.
Use the elevator.
Enter a door next to a fire extinguisher.
Fight some aliens and go up.
Shoot the window to break the glass.
Drop down in the alien habitat.
The blue pool can heal your life.
The green balls are ammo for a weapon you will pick later. They replenish over time.
Enter the passage embedded in rock.
Use the lift.
Pick up the green grasshopper looking alien.
This alien weapon is like a grenade launcher. The ammo it uses explodes on impact and is very powerful.
Follow the light down the corridor.
Pressing the red button will show a hologram of a scientist who will explain that they managed to create a barnacle weapon.
Enter the specimen containment room.
Go near the barnacle weapon to pick it up.
The barnacle can latch onto any organic material. Hold left mouse button to pull yourself towards the green goo that sticks to the wall. You can pull yourself towards any green goo you find.
Avoid the barnacle tongue.
Go to your right.
Go past the specimen observation area sign.
The tentacle aliens cannot be killed but you can stun them with explosives. Just try to avoid them.
Use the barnacle to pull yourself up to this hole in the wall.
Get in the vent.
You can use the radio here.
Cut the power from the lever.
Climb up and enter the vent with the propeller you just stopped.
More Half-Life: Opposing Force Walkthroughs
This Half-Life: Opposing Force walkthrough is divided into 12 total pages.