The objective is to locate all 10 keys required to unlock the exit door. They are hidden everywhere. Be sure to scan every space, including the rooms and passageways. Use WASD to move, CTRL to crouch, C to crawl, and Space to jump. The mouse cursor is used to aim, while the left mouse button is used to fire. To obtain additional tools and objects, press the F button. The scroll wheel can be used to change between firearms. To avoid having to approach the demons, try to attack from a distance.
Do all it takes to remain alive and escape the evil kingdom. Enjoy yourself and your luck!