Avoid getting any game over screens for the whole game; reload from a save file if you do get booted out of the hotel or get sent back to your room. If you manage to accomplish all this, you'll get an additional scene after the credits (after being asked if you want to save your game) involving the arrival of a certain character.
You'll get to an office in the game where you have to insert a specific combination to open a lock. The combination is 13-. (The last number will change from game to game). But it won't work, even if you know the combination, until you pick up the piece of paper lying on the floor near the cabinets in the room.