Deal with the three Ants in the area ahead and to the left; one may attack while you're clearing the rubble, so stay left while you do that. Run straight ahead and to the right to the ledge, then climb it and continue moving at the same pace, clearing the spider web out of your way with the Gravity Gun. As soon as the water area appears ahead, stop to avoid falling.
The next section of the cave will contain numerous barnacles hanging over the water, as well as antlions in the distance and one currently invisible spider. Position yourself so that the barnacles' tongues are between you and the enemy and set a trap for the monsters, enticing the ants to rush forward. Then, move away from the water's edge and await the arrival of your guests.
Two spiders will emerge from the end of the cave. They usually follow the ants, but if this doesn't happen, use the cover between the stalactites to avoid their acid spit and move into the affected area, then take out the enemies. Further ahead, there will be another stalactite with barnacles on the left and in the middle. Carefully navigate around this natural formation and continue running. Ahead, you'll encounter one Ant and a bunch of Spiders.
Hold off on running, recuperate, find the small tunnel on the left, and continue running until you have enough energy to reach the hole in the floor. An alarm will sound from there, and that's where the "Vort Ring" chapter begins.