Exit back where you came in and head straight down into the mouth of the cave. Kill the Tank, then tap the red computer panel in the wall to lowering the bridge across the lava pit. Watch out for a hovering Icarus or two. Once across, enter the doorway and proceed down the steps to the bottom. Kill the Tank and Beserkers and go upstairs where they are torturing a human to grab the health pack in the corner. Once back down, the doorway to the right will lead to the level 4 - the Torture Chambers. Enter here.