Nobody likes to be stuck so I made this walktorugh.

This content can spoil the game for you so only continue if you are stuck,
or completed the game.

Chapter 1 Awakening (intro)

The game starts with a combine assault on a base.
During this intro you will pass a room where Kleiner and Eli are working
on the experimental Zero Point Modulator (aka gravgun).
Then it procedes to a room with people in stasis pods, one being
Shepards pod


Chapter 2 Grand Escape.

Its been a few days since the combine assaulted the base and they are now
in control of the facility.
The G-man shows up and releases Corporal Shepard from his stassispod.

You have explore the area and evenually end up in a maintenance room.
You can see the crowbar in a ventilation duct, push the crate in front of
the ventilation and climb inside.

Make your way into the big ventilation shaft where you get a conversation 
with a  NPC. 
She tells you she managed to take the gravitygun before the combine got
 their hands on it and asks you to bring it to Dr. Kleiner in City 17. 
She also hints there is a buggy in one of the containers in the garage.

Pick up the Gravity gun and also check the supply crates before leaving
rough the ventilation duct she opened.

Going trough the ventilation duct you end up in a armoury, the doors
are closed but there is a machinegun lying one one of the tables.
While you go for the machinegun a Combine soldier will start shooting
you.
Kill the Combine and pickup the pistol if you didn't check the crates
in the ventilation shaft.

The tunnel you are in leads to the garage, but you can't enter if from there.
Check the other end and you will find a open door into the generator room.
Climb the big generator to the right and then higher into the ventilation duct.

You will notice there is a hole in the ventilation duct.
Use the Gravity gun to pull the grate  over the hole,
walk/jump over the 'bridge' you made and proceed.

You will come into a higher level of the big ventilation shaft.
The NPC hinted that the ventilation duct on this floor leads to the garage,
so enter the ventilation duct on the right.

When entering the garage you get into the first big battle.
But first notice the buggy inside the container in front wheb you leave
the ventilation system.

Its wise to stay at the ceiling and shoot advancing combine from
the pipes,but you can also jump down and shrow some obstacles 
to the enemy with the gravity gun.

Behind one of the trailers you can find a supply crate with health.
You will be short on ammo so pickup ammo from dead soldiers if needed..

Once the area is save you need to open the big gate.
The door to the gate control room is closed, you have 2 ways of opening it:
- Shoot the window if it isn't broken yet and throw in one of the explosive
  barrels, it will destory the barrier thats blocking the door.
- Go up the stairs, jump over the railing onto the little edge and
  enter the room trough the window.

Recharge your health, pickup the ammo and supply crates and push 
the button on the wall to open the big gate.
A alarm will sound and more combine soldiers will enter the garage.
Deal with thse soldiers, then drive the buggy out the container and go
outside.

More soldiers are defending outside, and they placed a combine gate.
Drive over the sentry gun and head back to the tunnel.
Step out, replenish your ammo  from the buggy's ammo crate and
go outside again on foot.  Immedialty turn left where you will see
some pipes that you can use as cover to take out the combine soldiers.

Onother tactic is to drive out with the verhicle, get out the verhicle and use it
as cover.

Once the Combine soldiers are death you must walk to the gate and press
the button at the left side of the gate to open the barrier.

Step back into the buggy and follow the road.
Just before the tunnel ahead there are some supplies at the base
of a lightpole.

In the tunnel the next level is loaded.

At the end of the tunnel you will run into a guardbooth with leverage
bocking your way, get out the verhicle, grab ammo from the buggy's
weaponcrate and try to kill the combine, using the buggy and
the truck as cover.
In truck you can find some extra supplies as well.

Once the soldiers outside are dead you can proceed to the guard booth.
Beware, there are still 2 remaining soldiers inside that booth.
Kill both soldiers and try to push the button bewteen the windows
to open the leverage.
Meanwhile a dropship is dropping extra soldiers, watch out for the 
dropship's weeapon.

Once all soldiers are dead and the leverage are open you can jumpback in
the buggy.

The road to the left ends in a destroyed bridge so go right.

When you get close to the car wreckage rollermines spawn in mid air.
Don't let the combine mines stop you,
just drive over those combine mines and with some luck non of the 
spawming rollermines catch up with you when driving trough.

If some did manage to attach them to the verhicle, you should stop in the 
halfopen tunnel and remove them with the gravity gun.

Proceed with the buggy untill you come at a big truck inside the tunnel,
get out fast and pickup the RPG launcher, deal quickly with the soldiers
at this barricade because a gunship will be joining the fight sooner then
you want. Once the Soldiers are death you can use the truck as cover
and fire rpg's to the gunship.  The nearby Van has a rpg crate when you 
need to reload.
You can also reload from the side trough the window whats much safer 
depending on the gunships possition.

Using the big truck as cover and show yourself  to 'pull' the gunship, when
it comes for you move back a bit and be ready to shoot when it flys by,
so it has no time to shoot back. Move to the other side of the truck and
repeat pulling and shooting until the gunship is destroyed. 

Once the gunship is destroyed you can clear the wreackages from the road 
by shooting them with your gravgun.

Proceed again with the buggy and when you leave the halfopen tunnel
you see a bridge with a lambda logo. Stop under the bridge and shoot
the wooden planks so the supply crates on top of it fall down.

Get in the buggy again and follow the road, you will pass a quarry and run
into a combine shield wall. You see a cable lead from the shield wall to 
the red barn at the quarry, return to the quarry by either using the door in 
the  fence, or the big gate near the river.

Kill the soldiers around and inside the barn, select your gravity gun and 
pickup the sawblades on the wall and place them in the middle of the barn
for quick acces.

Two dropships have arrived and are dropping combine reinforcements.
Kill them as they try to enter the barn, this fight can be pretty hectic.

Once the situation is clear you must figure out a way to disable the 
combine generator thats also protected by a shield.
You have 2 options:
- The easyest way is to use a barrel and place it next to the racks with
  granite plates, jump onto the barrel and then jump to the top of
  the racks. Jump now over the shield.
- Another way is to use a wooden plank to get on top of the racks
  but this is a bit trickyer and requires a sprint.

Inside the field you have to push the button to disable the generator.

Now the generator is down you can go back to the buggy and follow the 
road again. 
When you come on top of the bridge more rollermines willspawn but
just drive trough before their spawn sequence is done.


Chaper 3 Kilo Base:

Once past the level load, driving outside the canyon you arrive at
a soviet submarine base.  A landslide is blocking the way
Turn left and follow the sand road into the marine base.
 
On the left you will see a small structure with a lambda logo on it,
go inside, watch out for the headcrab and pickup the healthpacks.
A bit futher down you will see a oiltruck that just exploded blocking your
way.
If you look at the left side of the truck you have a g-man sighting.

Since the fire is blocking the road you need to find another way, moving 
back you now see a double door thats open.
Deal wit the enemy's and follow the stairs down.

A gate will block the tunnel ahead, pull the lever on right to open the door.
Follow the tunnel and kill the enemy's ahead, Use the gravgun to throw
the varioes objects.

At the end of the tunnel another door blocks your way, 
push the button on the wall at the right side of the door to open.

Kill the zombies and behind the elevator you will find ammo and supply
crates.
Take the elevator or ladder up. Watch out of the barnacle when using the
ladder.

You end up in a dark room, with headcrabs, zombies, a poison zombie 
and fast zombies, the rack has jerrycans that explode and
set the zombies on fire.

A blockade of crates is blocking your way to get outside,
zombies are breaking it, make a opening with the gravitygun if needed
and go outside.

When you come ouside you see a dock with 2 submarines. To the left
is a open door, but once inside the way is blocked by a headcrab canister
on fire.. 
You need to get on the nearby submarine. 

Some ways to get on the submarine:
- From the railing you can jump towards the submarine.
- From the wooden dock you can jump to a ruther of the submarine at
  the front.
- Move to the far side on the wooden dock and with the gravity gun
  you can lift the walkway to create a bridge.

Proceed to the back side where you can see a walkway that brings you 
to behind the building past the roadblock, 
enter the building and on the right is a door that leads to an indoor drydock.

Crates block the path to the left, use one of the varioes paths to 
go to the mobile power generator deeper inside the building.
Pull the lever and lights will go on and gates out of view will open.

Go deeper inside where you will encounter zombies in a loading zone.
Ones all enemies are death you can pickup the supplies in the locker
room. 

You now have 2 options:
- You can drive the buggy inside into the area with the poisonzombie and
  drive out trough the gate behind the burning truck from earlyer.

- Another way is to go trough the bureaus with zombies where you
  will find a door that also leads outside behind the burning truck.

You will see another  leverage further ahead with some supply crates.
When you are checking out the supply crates you hear a portal sound 
and can see some kind of portal being formed on the road to the right.

3 Elite combine soldiers come from that portal.
Kill the soldiers and you will notice the portal is still there.
Jump into the portal.


Chapter 4 Citadel Foundations.

You will find yourself in a portal tube, and the G-man apears, and bends
youre portal so it collides with another portal.

You then spawn in a huge shaft with a big elevator moving striders up.
On the other side is a ladder to climb, a door on the left and another ladder 
to climb.

Shoot the combine soldiers and move across the big shaft into a room 
 with 2 balconies and Combine shooting you.  
Right next to the door you came from is a button that brings down a small
elevator, use the elevator to bring you to the balcony where thers is a door
that brings you to the big shaft again.

After another ladder and mini elevator in the shaft you come to a control 
room  build in the sidewall of the shaft.  Kill the combine soldiers and run 
past the windows to the open door further away, avoiding the sentry gun
inside that control room.

Behind this door is a hallway with a wepaons rack against the wall.
When restocking at the ammo rack combine soldiers will assault you from 
the left

Follow the stairs up.

Another shield with combine soldiers block your way, kill them and go 
inside the big room to the left.

You now are inside the combines experimental portal room, seen in the 
portal on the previoes map.

A portal sequence is going on, all doors closed and the portal is protected 
by a shield. Meanwhile combine soldiers try to kill you.
At a higher ramp 4 elite soldiers are shooting you.

Once the elite soldiers are death the portal closes and a sound starts
to play.
At the origin of the sound you find a console with lever to switch.
A new portal sequence is started.

Something went wrong, the shield is gone and a large hole apears in 
the wall.

jump trough the hole and follow the stairs up again until you get back in 
the big shaft.
At the other side is a door that leads to some kind of combine airlock.


Chapter 5 Antlion Infestaton.

After the levelchange you can proceed tough the airlock, disable the 2 
sentry guns with the gravity gun.
It looks like the coimbine stumbled on something ancient when building
the citadell.

A cave with a tunnel is in front of you, the combine
cut a hole in the tunnel and placed some lights.

Following the tunnel you come intro a bigger cave  with some kind of
collapsed bridge.
Follow the tunnel al the other side of the cave and it will lead you to a 
generator room. 

Pushing the flashing button on the console enables the generator,
lights go on in the tunnels and a screen goes on showing you how 
the cave you just passed is taken over by antlions, rollermines and
manhacks.

Return to the cave, the antlions broke the glass tunnel at the side, use
the pipes to get there.

Follow the tunnel and another small cave with pods moving around apears.
One door leads to the generator you were before, the second wont't open 
and the third brings you eventually to a control room.

Push the flashing button on one of the console again and you see the
doors open on the screen.

More antlions come into the control room to fight with you.

Go back but watch out for the antlion guard breaking trough a door
near the control room.

Return to the cave with moving pods and go trough the door
thats now open.

Follow the tunnel and you get caught in a weaponstripper sequence that
overcharges the gravity gun.

Then you end up in a huge cave with more pods moving around.
At the end of the tunnel is another control room with flashing button, when 
you press this button a explosion takes place and a part of the ceiling has 
collapsed. You can see how the antlions escape to their freedom.

Since there is only one way in and out you go back to the tunnel where
a ingame sequence takes control.
Dr. Breen comes running in with 2 Elite combine soldiers giving a speech 
how these antlions won't stop the combine invasion, only slowing them 
down a bit.

Before Breen can do anything the G-man ports you out for a 'debiefing'
And so ends the game with the.credits.