The Bio-Research Facility
Walk forward and down the steps into the garden area. Follow the path to the left and speak with the man. After the conversation, search the planters for ammunition, though be careful around the plants--they bite! Walk into the fountain in the center. Pull the statue head to open a passage. Locate the passage to the right of one of the staircases. Enter the passage into the room on the right. Climb the ladder.
Pick up the ammunition and pull the switch, which opens another door. Descend the ladder or just fall down. Go up the opposite stairs and into the small room. Push the yellow button.
You enter a room with many tubes--one has something nasty inside, which breaks out as you enter the room. Equip a weapon and eliminate the beast. There are more awful things in this room; the enlarged insects emerge from the left and right sides of the room. Terminate them all. You may need to switch targets to survive; press the square button to do so.
Go up to the second level on the left side of the room. Go to the middle of the level and look for the overhead pipe. There's also ammunition up here in the far corner. Traverse the pipe all the way to the upper middle of the room. You can drop down on the walkway there. Go to Lara's right and turn the valve. Follow the catwalk to the other side of this area, using small hop jumps to get over the break in the platform. Turn the other valve. This opens the flooring in the busted tube. Return to the pipe and traverse it back to the side of the room. Drop into the busted tube into the next area.
Climb out of the sludge. Slide down the ramp in the next room; jump as you near the ramp's button and grab hold of the ladder against the wall. Climb up and grab the health pack. Open the door. Ascend the staircase to the door at the top. Enter the door into the next area.