Kill the frogman before attempt to get those harpoons. Then you can proceed down the underwater tunnel until you can climb out onto a ledge and take the medkit. Slide down the slope then hang and drop to the floor which breaks away dropping you even further.
Kill the workman and guard in this next area and claim their medkits and Uzi clips. Pull out the moveable box in this area to uncover a few more moveable boxes. Continue to move the first box until it is in the hallway. Now you can push and pull the remaining two boxes until you reveal two concealed passages.
Look for a hole in the ceiling on the other side of the room. Climb up and kill a patrolling guard up ahead and the other who sneaks in from the rear. Take Secret #1; the Stone Dragon from the hole then return to the two passages.
The left passage goes to a locked bathroom so take the right passage to the Ballroom and kill the workman and the guard on your way. Feel free to take their medkit and flares before entering the Ballroom. Watch out for the deadly glass as you take out the guard on the second level. Move around to the side of the hole where there is no glass then step back and run into the hole letting your momentum carry you to the ledge below.
You should easily find the Bathroom Key nearby before making a return jump to the side of the hole without the glass where you can pull back up to the Ballroom. Return to the left passage which leads to the bathroom and use your key on the lock behind the chair. Push the button to open the double doors and kill the workman who comes charging out. Go through these doors to find and push another button to open the door on the second level of the Ballroom. Go back and press the other button to shut these doors before leaving.
Back in the Ballroom, drop off and shimmy to the left to reach the open door. Now you can take the ramp to the right of the door up to the second level. Take the ammo from the guard you shot earlier then continue on until you can do a running jump to grab a ledge which has Circuit Breaker #1. Take it then return to the door.
You should now be in a hall with several doors. The first door on the left leads to an empty room but open it anyway. The only other door you can open (right now) is the door on the right with the wheel. Spin it to open the door then enter and drop to the floor. Move the box until you can reach the switch then use it to open the door above. Move the box up there so you can reach the door. Continue through the next room and up the ramp to deal with another guard, then head for the next room which has a box in it.
Move this box so you can reach the switch above and take the Rusty Key that was under the box. You can now return to the hall and use the key in the door opposite the open door to the empty room. Enter and drop to the floor and move the box so you can pull out the box above. After you pull the first box and push the second one, you should find a passage to the right. The floor will break away here and there are also barrels which will roll over you if you try to simply dart across the collapsing floor. Instead, run a sweeping arc to collapse all the panels while avoiding the barrels. You should end up where you started.
Heavy breathing should tip you off that another bad guy is lurking in the vicinity. Head around the left corner and take care of the guard then return to the tiles where the barrels came from and go get Secret #2; the Jade Dragon. This is tricky as a lone barrel is waiting to crush you. Jump up to the sloping passage and as you pull up you should hear the approaching barrel. Jump back then to the left to sidestep the barrel then you can proceed up the passage to claim your statue.
When you arrive at the room with the grate floor and a boat below you need to drop down to the boat and flip the underwater switch over by the ladder. This opens a timed door up above so get back on the boat and pull up to the floor above and run through the door. Flip the switch you find in here to permanently keep the door open, then begin a series of jumps between the two sloped areas. Keeping jumping until the pit below closes then you can stand and pull yourself up into the opening. Flip the switch to open up a section of the wall back past the area with the boat.
Return to the newly exposed area and kill the workman and the guard then push the button on the left to open a timed trapdoor. Run around the pool and dash through the trapdoor before it shuts. Go get Circuit Breaker #2 which is down to your right. Taking this item opens the exit which is also on a timer. Grab the medkit then go and press the button on the wall to drain the water where the boat is. Trip the exit open again and return back to the area with the boat. Jump down onto the boat then spin the wheel to open the door.
The passage leads off to the left where there is a trapdoor to the Bathroom. The double doors should form a bridge for you to cross over and get Circuit Breaker #3. If the doors are open you will need to go past the trapdoor to find the button which shuts them. Now with all three Circuit Breakers, drop down into the Bathroom and kill the guard and workman and take their ammo and harpoons.
Return to the pool room from the beginning of this level and get the medkit from the corner of the room. Take a deep breath and swim through the passage and flip the switch at the bottom of the tall shaft which will open the door up top. Now swim up and out through that door and kill the worker, guard and boss. Use your M-16 to kill them quickly then take their medkit, shells, and Uzi clips. Plug in those breakers into their slots then move the box under the opening above and climb up. Take care of another workman then flip the switch to flood the room up ahead. Jump across the overhead ducts to reach this area.
Follow the passage and kill the Barracuda when you wade into the water. Grab those harpoons over to your right then head through the exit to the dark passage on the left where you can kill another worker. Make a note of the Cabin Door then continue left to find some ammo. In the room with the windows you need to spin the wheel to open the door. Enter and flip the switch then run to the other side of the room through the timed door to get some flares. Push the box and use the switch to open the trapdoor at the end of the hall.
Go to the trapdoor and jump into the ocean. Climb out and wait for all of those dangerous underwater obstacles to start swimming towards you. Wait for most of them to appear below you - which means they aren't guarding the key - then jump in and begin the race for the key. The fish are fast swimmers so try not to make and drastic course changes. Swim through the opening up ahead and turn right. The windows should now be on your right and the Cabin Key lies behind the rocks on the left.
Dodge the shark while getting the key then make a sweeping circle back around toward the opening you swam through a minute ago. The pack of fish should still be pursuing so head for the opening. As you exit through the opening look for a cave opening across from where you exit. Swim into the cave and stay along the right wall until you can see a small opening above you. Swim to the surface and breath and take Secret #3; the Gold Dragon while you rest for the final race back to the ship. When you are ready, dive down and exit the cave and return to the trap door dodging the fish as needed.
Climb up through the trap door and turn left and return to the Cabin Door and use that key. Enter and flip the switch to open a trapdoor outside. Now go push the box to flip another switch before returning to the cabin where an opening in the ceiling should be waiting. Climb up and proceed down the passage until you drop into the next room. Make your way around to the right to the hole in the floor. Turn and run into the pool room and stop before you go in the water. Kill the guard and the boss and take the M-16 ammo. Dodge the shots of the frogmen from below and if you need it, go get the M-16 from the dark passage.
Kill the frogmen then jump into the water. If they refuse to make good targets then jump in and tease them then climb out and shoot them when they eventually surface. When both are gone dive in and move the barrel to reveal the passage which leads to the exit....