To begin with, jump across the lava. Don't get the medi-pack.
Get the uzi and jump across another ledge.
D-O  N-O-T go under the spike balls. Advance through the
corridor carefully and go under the spike ball
with the item. Carry on and get the item.
Combine the two items and put them in the door
in the room in front. KILL THE NINJAS!!!
And enter the water.

Swim to the tunnel in the corner. Grab the
shotgun and crossbow. Advance through another
tunnel and exit the water.

Run through the tunnel. Don't sprint, don't
jump, just walk or run. Go to the room with
the big slope and through the tunnel to the
left.

Wade through the water and get out. Kill the
scorpions. Shimmy over the lava and drop
down at the end.

Go through the planty room and drop through the hole
at the end. Climb up the pole, slide down the slope and climb the ladder.
Step on the purple square.

Swim back through the level. There are a few
air holes:

1) In the room with the big slope, it's at the top of the slope.

2) In the room after the ninjas In the middle area, at the top.

End) In the first room, at the start. Up.

That concludes the walkthrough. Good luck!