I have finished to write a game guide for anyone who is stuck is some puzzle or have problems with any part of the game.
Link: http://www.uroborostudio.com/guide
The guide is divided in parts corresponding with each zone of the castle. Click on the spoilers buttons to see the text.
It has a step-by-step description of the game puzzles, what items to locate, how to use it and where to go. Also a few tips for combat and boss fights.
It contains spoilers, so use it at your own discretion.