Not only do you need to find some air - you also need to out-swim a Great White Shark who has selected you as its next meal. Spin around and start swimming behind you, following all the junk on the ocean floor. When you arrive at the ship, swim into the hole where the anchor is protruding and find the air-pocket so you can breath. The shark is still coming so when your lungs are filled dive down and swim into the hole below and angle off to the right.
Head up and into the large room then enter the opening on the left and continue on into a smaller area and take the next opening on the left. You should now be in a room with a patterned floor so head left and swim down towards the metal girder and flip the switch to open a door in the floor behind you. Swim through this door and go left and follow the passage until you see a hole above. Surface to finally catch your breath and climb on the box that is floating here.
Head for the pile of boxes on the right and swim into the small opening in the middle. Climb out and head to your right. At the end of the dark hall is a switch so flip it then return to the stack of boxes and climb them to enter the next room. Drop down to the floor and kill the workman who tries a sneak-attack from behind one of the boxes. Grab the shells from your enemy being extra careful not to step on the dark area of the floor which is a giant trapdoor.
Secret #1; the Stone Dragon is just sitting there for the taking, so go get it while avoiding that trapdoor. Once you have the statue you can jump over the door which will cause it to open. Now you can kill off all the bad guys from up here before dropping down to the closest box to pick up your spoils; a medkit and harpoons. Now climb on the box in the middle of the room and jump to the higher box along the wall so you can climb into the opening and enter the next area.
When you enter this next room flip the switch to your immediate left to open a timed door near the windows. Run and jump and enter the door (the timer will stop when you are in). Dive down to get Secret #2; the Jade Dragon while avoiding those pesky underwater creatures who would try and stop you.
Lara now needs to get past a long row of timed burners which line the hall. Here are explicit directions for getting past the hardest puzzle encountered so far. Start down the hall and turn into the dark passage and climb up into the hole in the ceiling. Flip the switch to open the door next to the hall with the burners. Enter that door and get ready for the race of your life. Saving wouldn't be such a bad idea.
HINT: When racing through this puzzle make sure you jump over the beams and even the short walls which lead to the rooms with the switches. If you try to climb or even stumble, you will lose precious seconds that you don't have.
Flip the switch to turn off the first set of burners which lets you run as far as the next switch. Flip that to open the other door then run and enter that room to flip another switch. All burners are off for the moment so run all the way back to the first switch to turn off the first set of burners. You should now have plenty of time (or about 10 seconds) to run the entire gauntlet of burners and arrive at your next puzzle.
Go into the water and kill the Barracuda. Now get ready for a puzzle almost as challenging as the last - only this time it's UNDERWATER! To sum it up; you need to swim through several underwater rooms, flip a switch in the third room then swim to the bottom to flip another switch which opens the hatch up above. Secret #3; the Gold Dragon is also at the bottom in a tunnel by the switch. And if your running out of air wasn't enough - let's throw in a mess of Barracudas with an attitude which swarm in when you touch that statue. Sound like fun? Good - Go for it!
HINT: Always slow down when making underwater turns, and always do the Reverse Roll to back away from switches after using them. You can also skip the mini-movies by pressing Lara's "look" button to save valuable seconds. And if you just can't manage to get that statue, you can always surface and fill-up on air before diving back down to get it.
Drop down into the next area and survey all the rocks and junk in this room. Find and drop through the hole in the floor then find and pull the box so it is under the opening. Now you can climb up and use the switch which will dump all the rocks from above down to this level. You can now reach two new opening and a door opposite the switch. Make your way to the opening on the right and climb up to reach the previous level. You can only grab the ledge that faces center of the room below to do this.
Staying along the left wall and go into the opening above. Use the switch to open a door somewhere else in this level then drop all the way down to the lower level and this time climb up into the left opening. Keep along the right wall until you can climb up to a flat ledge. Do a running jump to land on another ledge on the left. Climb up into the opening above to find and flip another switch to flood an upcoming room.
Once again, return to the lower level and this time enter the door and follow the passage to the room you just flooded. There is a door below and a frogman in the water so dive in and kill him with the harpoon gun. After you eliminate this obstacle, continue through the passage and get out of the water fast. A workman and a Rig Boss are moving in for the kill. When they are dead you can take their medkit, shells and 2 packs of harpoons over in the corner. Use the switch on the wall to open the door and exit this level...