So, it can be possible because doors in this game is not perfect parallelepiped but a low-detailed convex parallelepiped. After some practice you can jump on some polygon and, use it like a ground, jump on edge of wall or fall into location nearly you. It helps you to skip most location in this game and now you don't need find a keys for open a doors.

How to do it? Open a door and stand in face-to-face. When it starts to close try to jump on it but don't stop press on space or you will fall on the ground. Move straightly because if you fall between rooms you will die. Also it can be if you not enough lucky when you tried jump on the upper floor, so be carefully.

How to skip fight with Nosferatu? Unlock the door into a Main Castle and jump into a portal. Go up the stairs to light's right amplifier. Jump in space between ground and you will be outside the location. Move behind a corner and keep going forward but not closer to room 'cause you will fall into a room under you and die, and not far 'cause you will be stuck in space and die too. When you will come to the wall, drop your sword for find a place where you can jump on it and jump outside a location. Now move to light and prepare for your last fight!

Good luck!

p.s. sorry about my English, i'm not really be good at this.