Half-Life 2: Episode Two/This Vortal Coil

Defense
After stomping on the two grubs, you will reach a chamber with the vortigaunt and two members of the resistance (Sheckly, the soldier, and Griggs the medic). They will explain the current location, providing information on how to set up defenses.

The area has four entrances. From left to right, the Breach (a burrowed tunnel by antlions), 36 (where you entered), 12, and 24.

There is a shotgun ammo crate between the breach and 36, and an SMG ammo crate near the forklift at 24. Mines are located to the left of the breach, as well as left of 24.

You may want to pick up the SMG near the vortigaunt, although the NPCs will let you know.

The place was quiet before you showed up, and the antlions are chasing after because of your progression on the Get Some Grub achievement.

Waves

 * 1 light from 36.
 * 1 light from the breach.
 * 2 lights from 24
 * 1 light 36, 1 light 12. Sheckly and Griggs will cover 36 - move the turrets over to 12.
 * 1 light breach, 1 light 12, 1 light 24.
 * 1 light breach, 1 light 12, 2 light 24.
 * 1 light breach, 1 light 36, 1 light 12, 1 light 24
 * 1 light breach, 2 light 36, 1 light 12, 1 light 24. Both turrets break during this wave.

At this point, 3 lights appear on 12. You will see a few dead antlions falling, before vortigaunts arrive. Use this time to plant any remaining mines

The final wave will have 3 lights on all tunnels. The antlions will swarm, but are cut to shreds by you and the reinforcements.

Antlion caverns
After stepping on the two grubs after map transition, your count should be 91.

You will proceed through a short tunnel into a chamber. There are several antlions in a group; you will see a new attack that stuns the antlions, and you need to quickly kill them when they're in that state. Watch for acid antlions trying to snipe at you. They will attack after the initial volley, and again when you head around the loop. The vortigaunt will tell you that the acid antlions allow the quick carving of the tunnels, as well as a deterrent for robbers.

Count should be 111, including the two on the ceiling.

Another chamber with antlions. After this, head down the tunnel to get the third cache. Count should be 126.

The next section is a tunnel, with a few acid antlions. Keep watch on the ceiling to look for the fourth cache on the ceiling - but be careful as opening it will drop a live grenade. Count should be 134.

Now, you should return to a regular mine section. The wooden floor in the middle will collapse when you step on it - there's nothing of importance down there. You'll have to open a door barred by wood by disloding the pieces with the gravity gun, and destroy the zombies. There is a gate blocking, and to the wheel for opening the gate, you need to go down the lift. The lift, however, is raised by a counterweight, and to get down, you need to place a few heavy items on the lift. (If it stalls while going down, try jumping a few times.)

After going down the lift, count should be 143.

This area is covered by zombies. After killing them, you should see a lift back up, but it's not designed for a single person. Weigh it down with the two I-beam bundles below, the I-beam bundle in the corner and a barrel near the counterweight, then press the switch to start the lift, and push the weights off. Destroy the zombies that are nearby, and open the gate. The vortigaunt will then activate the generator to open the nearby door.

Count should be 161.

Next, you should see some crates near the abyss. Grab them to boost your armor, but be quick with the ones strapped down - they will quickly fall into the abyss below. Proceed onward - when you are near the grubs, you will be attacked by zombies, one of which will somehow push a cart towards you. Proceed up the ladder, and push the metal container with the gravity gun (a crate is inside) and jump down the hole. You will take a quick ride down a cart that smashes through a few zombies into the water below. When you climb back out, you will see the vorigaunt has already taken care of the other opponents; take any remaining supplies and then head into the antlion tunnels on the left.

Count should be 196.

Across the chasm should lead to a small area with an antlion repeller. Kill the antlions and zombies and secure the area. collect supplies and press the button next to the lift to call it. Zombies will break out of the buildings, and engage while the lift approaches. When it arrives, climb on it, and the vortigaunt will wait behind for a few seconds before taking the second lift. The zombies and antlions will continue fighting eachother.

Count should be 213.

After passing into the mines, you will see the glimpse of the ancient guardian. it will smash a few beams before running away. Adance into a different tunnel, knocking the support beams out behind a grate. Go forward from that gate and take a right - repeat knocking out the beams and advance.

Antlion lair
You will approach the lift that connects the bottom of the pit with Alyx Vance. You will have to jump down to the platform visible within the shaft, unblock the fan and when it stops, spin it with the gravity gun; you have to hit the fan at an angle to do this. Proceed down the tunnel, and jump down the hole into the water. To proceed, you need to swim through the central column to the other side of the stalagmites. Careful with the ropes; those are barnacles that want to pull you up. The exit is a small yellow tunnel.

At the exit of the yellow tunnel, count should be 244.

The next portion is a ring, with a few acid antlions. Get health from the local area as well as making sure your count is 248 before jumping down.

When you first see the ancient guardian, it will charge towards you and smash the stalagmites. At that time, sprint to the other side and dive into the yellow tunnel. When you reach the other end, the guardian will smash the obstructing rocks, take a look at you and head down the tunnel. Wait for him to leave and make a sprint to the left to the next tunnel.

After this second tunnel, the next exit is to the right and is in clear view. Sprint to it. Go through the tunnel and you should be on a bridged pit. You need to slip past the guardian this time; get him to approach, and sprint down the corridor to the right and into the alcove. Exit the alcove to reach a ring room. Count before jumping should be 285.

Sprint into the yellow tunnel within the ring, and exit by the web on the other side. Sprint to the left until you see a boarded area; break it open and jump in. The guardian will try smashing it open but fail, and instead breaks open the floor. Count should be 296.

You should now be on the lower floor of the elevator. You can find cache 5 (on the entrance wall to the right), 6 (on the ceiling in the middle), 7 (on the ceiling above wooden planks), and 8 (wall on the right) here. Grub count is 311.

To activate the lift, you need to get a gear located within the water and place it on the motor (although a barnacle will try to pull the gear away). Press the button to call the elevator.

The vortigaunt will proceed to the Antlion nest and collect the larva extract. Return to the elevator when you are done.

Grub count is 315. (Achievement is awarded when you kill 333, and there aren't any other grubs beyond this point.)

Alyx Vance
Heading up the elevator will return you to Alyx, where the vortigaunt will use the extract to revive Alyx.

During this, the G-Man will appear, in a cutscene where he informs you about his decision to preserve Alyx, and gives her a message to relay to her father. She will then awaken and, with assistance, enter the lift. Follow her.

After going up, you will notice the guardian is enraged by the theft of the extract. It can't reach you yet, but will soon. Jump down the hole to proceed.