Hang a left as you being this next underwater level and pull the lever to open the trapdoors ahead. Enter and cross the next room taking care of the crewman on the way. Jump to the flat area to find a switch up above. Go to the other side of the room and out through the opening. Continue down the passage and eliminate the workman and the guard and take the harpoons for your efforts.
As you exit the passage you will need to backflip to avoid some barrels then kill the crewman who arrives on the scene. At the top of the ramp, grab onto the ledge and shimmy over to the switch and use it to turn off those burners. Head to the left and enter the next passage to find and use another switch. Drop through the hole to arrive back at the piston room.
Jump and grab to reach the first piston then begin to cross over the rest of them. Kill the guard up ahead then turn right to do a running jump to get to the ledge with Secret #1; the Stone Dragon. Once you have your prize, do another running jump and grab and pull up to continue.
Follow the winding hall until you reach a box which you can push to open the way to a second box. Push the first box two more times then you can move in to push the second box. Drop down through the hole to flip the switch then jump back up and grab and pull back up to the box area. Return to the pistons and climb back across to the other side. With the pistons in their new position you can now reach the ledge to the right. A running jump with a grab should let you pull up and flip the switch to flood the room with the burners.
Return to that room and pull the lever which opens the door. Swim through the door and kill the frogman on the other side from the safety of the room to the left. When he is dead and your lungs are filled you need to open that trapdoor in the ceiling of the large room. Swim into the cave and head left. Try to keep to the left side of the cave and the Giant Moray Eel may just not kill you. Flip the switch then head for the trapdoor. Stay out of the moss or you will get tangled and drown.
Kill the guard up above as you exit the trapdoor. Use the switch to open the door on the opposite side of the catwalk then enter that door to find two switches. Flip the switch on the right then immediately flip the left switch to raise some metal devices behind you. Flip the first switch and jump right then left then throw the left switch. Reverse roll, then run and jump forward and grab to shimmy to the right until you reach the ledge with the switch to open the trapdoors.
Head for the corner where the trapdoor is. Facing the lower slope, do a series of jumps between the slopes to grab and pull up to the top ledge. Cross over on the ducts and move the box out of the way. Shimmy past it and continue along to the large metal beam in the center of the room. Continue along the ducts until you can jump into the opening in the wall on the other side. A workman is to your right so take care of him before proceeding.
At the end of the hall go to the area where the workman came from. Below is Secret #2; the Gold Dragon which is protected by deadly glass, so jump over and pull up into the upper area and fall through the floor. Take the statue and walk through the deadly glass until you can pull yourself back up to the hall.
Continue on and slide down the ramp and shoot the Barracuda which waits in the pool below. In the corner is a collapsing panel which leads to Secret #3; the Jade Dragon. Stand on it just long enough to have it start to break then pull up and kill another pesky fish before swimming through the opening to collect this level's final secret.
Use the pillars to make your way to the top of the slope. Watch out for the collapsing floor between the two pillars by the window. Immediately jump to the taller pillar before you fall through. Shimmy across to the right and pull up. Continue up the slope and drop into the hall and kill the guard up ahead on the right. Proceed down the walkway and kill another guard to your left. Pull the box at the end of the room to open the way to the Theater. Head back and jump over the balcony.
Kill the crewman and the guard who appear below the balcony. Drop into the pit where these bad guys used to be and move the box to reveal the Theater Key. Push the box back to climb out and kill the boss who has just arrived. Head for the Theater and kill the crewman who is to the right of the theater door. Enter the theater and kill another crewman to the right unless he was already waiting behind the door in which case; kill him where he stands.
A boss and crewman are on the right balcony so kill them and flip the switch nearby. Then go pull the curtain on the stage and kill the workman. You may want to light a flare to find the button across the pit of glass. Press it to flood the pit back in the previous room where you found the Theater Key. Return to that area, killing another boss on the way. With the pit full of water, you can now make it across and enter the passage and exit this level...