Level 19. Water Torture

Start in front of the burned place. Grab any items and dive into the water in the center of your (minimap (the small circular map in the bottom-left corner of your screen) - a small map displayed on your HUD (heads-up display — the on-screen icons showing health, ammo and the minimap)).

Look for a vent in front of a small medikit. Go through the vent to reach the other side.

Go through the opening and dive up. Jump out and kill the ninjas attacking you.

The lift ahead requires the red key, and the door next to it requires the yellow key. Go through the other door and kill the ninjas.

Jump to the "10" Submarine and kill the ninjas there.

Jump back up the way you came in, set your compass to East, and jump there. Kill the ninjas.

Locate the red-lit room next to the red cabinet. Jump down and kill the baby rippers.

Proceed through the door ahead to find a girl with a mechanic screwer and moving columns. Investigate the non-moving column; it will descend, granting you the BLUE KEYCARD.

Make your way back to the blue key door, located right where you exit the red-lit room. Use the BLUE KEYCARD to open it and proceed down the blue corridor.

Enter the first room on your right, the bedroom, to find items.

On top of the bedroom, locate vents. After exploring, hit the fuel tank to flood the corridor. The doors will lock.

Dive back up for oxygen if needed. Swim back to the bedroom, face East, and go up to the vent for the RED KEYCARD. Another vent nearby contains sticky bombs.

Return to the red key lift using the path described earlier. Use the RED KEYCARD on the lift and take it up.

In the computer room, kill all the Rippers. Grab the GREEN KEYCARD. The other door is locked due to water.

Go back to the outside of the BLUE key door. Set your compass to NorthWest and head there.

Go through the door, kill any enemies, open the next door, and kill the Guardian.

Take the first left, go South, and turn right to find a ladder. Climb up, turn left, and use your GREEN KEYCARD on the "Authorized Personnel" door.

Kill the Shadow Ninja inside and collect the shotshells and fortune cookie. Hit the switch to activate the lift.

Head back out and jump on the lift to reach the previously inaccessible area. Kill the Guardian and the enemies in the next room.

Pick up the YELLOW KEYCARD. The yellow key door in front of you leads back to a familiar area.

Go back to where you rode the moving lift. Use the yellow key on the yellow key door there and proceed.

Hit the switch down the yellow path to make the lift rise. Take the lift down and kill the Coolies and Shadow Ninja.

Find and use the remote control to blow a hole through the steel door with a crack in the middle, visible through the window.

Swim back under the "10" Submarine and through the hole you created. Grab the grenade ammo and swim up.

Kill the two Serpent Gods shooting fireballs. Jump up to the path, hit the end level switch, and complete the level.