No love from the elevator
Climb the ladder and find the next obstacle. Climb the railing, crouch, fire the gravity gun at the bottom of the bell, then crawl to the hole and drop down; you'll end up in a mine cart and be sent down a slope into a very deep pool. Miraculously, you'll survive the fall without any damage, then surface and emerge onto dry land. Try to remember to grab the fuel barrel before you leave the tracks; I almost always do this after leaving, and Steve isn't helpful at all. Follow the narrow path with the ledge into the elevator cavern and explore the area.
(NOTE) There's a major melee ahead. From your current position on the ledge, you need to cross to the opposite side of the cave to activate the elevator. Once activated, it takes about 60 seconds for it to be ready. Once activated, I attack the flip-flop/defense for the next minute, taking out hordes of ants, zombies, spiders, and headcrabs. Just keep swimming... moving, taking advantage of ammo in the form of health packs, fuel barrels, and mines located throughout the vast cavern until the elevator arrives. Run when Steve yells "SAVE YOURSELF."
The elevators are on the opposite side of the cave, at the ends of each short tunnel with a health pack in them. Several canisters and barrels of explosives are scattered throughout the cavern world. If you don't get off the ledge and they're in Steve's line of fire, he'll do his thing and dismantle them. If you pulled out the Gravity Gun, use it on the local group of enemies, then jump off the ledge and run into the elevator on the raised concrete platform. Clear your path with the gun as you go; Go right from the elevator cage and press the button, then drop down from the platform side. Keep moving and grab the explosive canisters with first aid kits.
Use your pistol to detonate explosives from a distance if a group of undead is gathered ahead near the barrel. Otherwise, use the Gravity Gun to throw fuel into the crowd to draw them closer to the main group and detonate them from a distance. Groups form when ants, spiders, and zombies block the passages. Don't use the Demolition Tool if you don't have enough range and something is approaching ahead. Steve will let you know when to take a break before the elevator, quickly switching to his assault rifle, readying it for the ants and spiders all the way to the top of the elevator. Search the room for items using the Gravity Gun, and then wait for Steve to start the generator. The enemies will definitely reach the railing outside the generator room from the ground.
Follow the tunnel to another hole in the floor and drop down. Steve will warn you about a guard who is just trying to break through the wall, so you will have to run from him for a while.
Running through holes looking for nectar
Continue along the tunnel to the next ramp, find a path near it, then jump onto the ledge leading to a large slope. Figure out how to avoid certain death and secure passage. I approach the fan, its coils, and interrupt its rotation with the gravity gun to slow the speed and set the fan blade's "gap" position for passage. Find the next hole in the ground, remove the web, and jump into the water. Watch out for barnacles and stay close to the grotto perimeter wall for safety as you move to the exit point.
Look through the larval tunnels for a spider x1 waiting below in a larger tunnel; it's one of many if you let yourself get caught in their horde. The best solution I have is to ignore them as much as possible and blast anyone in your path with the gravity gun before they can spit back. So, wait for #1 to spit; he'll usually retreat around one of the nearby bends in the tunnel. Wait for the attack to hit the tunnel wall to move to the exit point. If #1 doesn't leave and is right in front of the exit, return to the tunnel and throw a grenade, then switch to your assault rifle and finish off the survivors.
(NOTE) No matter which direction you go, you'll be dealing with at least two spiders either way.
Run to the first bend, climb the opposite wall of the tunnel, and fire the gravity gun at the first enemy, then search the area for them while switching to your assault rifle and grenade launcher. If the area turns out to be empty, so much the better, as #1 has gone the other way. Spider #2 should be visible further down the tunnel; run towards #2, dodging his spit until you're close enough. As soon as he spits, shift-speed towards him and blow up #2's stomach with the gravity gun, and if that doesn't work, finish him off with the machine gun.
Exit the tunnel, then return to the wall; Dodge left or right along the wall to look at the room far away and find the Green Guardian. Wait behind the stalagmite, defending from his attack. Run around the ridge and away to the next tiny hole in the tunnel when the Green enters it. The tunnels are a route, a safehouse with supplies and larvae. Enter and quickly go through tunnel #1, drawing the gun when you approach it. From #1, run left to tunnel #2 until you can stand safely in the tunnel and be sure to remove the web at the entrance. Exit #2; sprint to the 2nd hole in the ground leading to Tunnel #3. And from there to #3 before the Guardian moves into the area.
As in Tunnel #2, move until you can't stand, tearing apart the exit point's nets with the cannon. Be careful, as the Oaf will likely throw boulders at you in this room. Keep an eye on him at all times; whenever you're unsure where to go next, listen for the Guardian to move behind the stalagmite; that's the time to move. Press Jump while forced to sprint 40-50 feet from Tunnel #4. You can't miss it (there are two maggots nearby). The last time I got hit, I missed the entrance to Tunnel #4; #4 is cover, not a tunnel. Quickly enter #4 deep enough to avoid the attack. The Guardian will stop at the entrance and gallop along the previous tunnel.
You can reach the Entrance when the monster dodges, approaches tunnel #4, turns, and disappears around the corner. Go left and run to the tunnel fork, switching to machine gun. Run straight at the fork and go through both spider tunnels. You should hear Green jumping halfway between tunnel #2 and the boarded up exit on the right. Be prepared to dash the last 40 feet. As you approach the right side of the exit, fire a 1-shot grenade launcher into the space between the top and bottom boards on the outside, placing them so that both boards break. Fire a 2-shot grenade launcher into the inner diagonal board when you stop before the exit, and then a 3-shot grenade launcher into the top/farthest part of the small room. Quickly move and drop through the gap in the floor to avoid damage from Green.
Enter the next cave; I head straight to the opening to grab the revolver and machine gun ammo. Clear out the debris, find the missing gear, and return to the elevator lever. Take out the barnacle that appears from the rubble and carries off the finds before carrying out his plan. Go into the elevator, press the button, and collect the loot and supplies while you wait for Steve. Next, follow him into the larval hive, then return to Alyx and the others. Once the ritual is complete, enter the elevator and find the final opening you'll need to go through in this chapter. When you fall to the ground below, you'll find yourself in Chapter 3: Freeman the Bridgebuilder .
Source: www.gamefaqs.com.