At the main menu screen enter the code

To obtain some of the hidden weapons in the game, you must complete the missions with a Silent Assassin Rating to receive that weapon.

Go to level nine, The Wang Fou, incident and go in the restaurant. Hop on the elevator on the first floor and take it down to the basement. Work your way through the tunnels (you won't have your map) killing any guards you encounter. At the end there will be an elevator. Head up to the mansion's first floor and flip on your night vision goggles. Wonder around in the dark until you find stairs that go up to the second floor. Once upstairs find the office and on the desk you will find Orthmeyer's Keycard. Go back down to the basement and head back upstairs to the first floor of the restaurant. Finish the level like normal and save.

Now exit to the main menu and start Mission 1 - Asylum Aftermath. Now find the first key card door. There will be a patient pacing back and forth with the mini gun, kill him and take it. You'll be walking much much slower now because it weighs so much. Find the second keycard door in the basement to get the duel gold desert eagles and finish the level with those two guns in your inventory. Now sit back and enjoy the fruits of your labor.

Complete the Training with Silent Assassin rating to unlock the Cardboard Tube. This weapon works like a sword, with the exception that it can attack enemies and launch them away!

When you die, there will be a black and white death sequence. If you were able to commit at least 4 consecutive head shots on 4 different guards, you will be able to resume what you were doing with a small amount of health.

In the training level, enter the complete level code to complete the level with an SA ranking. Then, re-enter the training level to find that your weapons storage has been completely filled with all the weapons in the game.

If you can sneak into the sauna area, you will see a guard. This guard will patrol the area, trying to protect Fritz. CAREFULLY kill, of anesthetic him. Once you have taken care of him, SNEAK down the small set of stairs into the pool and fiber wire Fritz. (Fritz makes rounds of going to the bar, sauna, and the pool.) If it works well, you will see a "cut scene" showing 47 drowning Fritz

Just hit L1 to pop up the Map. When someone shoots at you while your Map is up, you'll be able to sustain the damage and not get hurt until you take off the Map. This does NOT work on the Professional Difficulty.