Because the Structure of the game is largely non-linear, the walkthrough is broken into a few sections. The Introduction section describes the opening puzzles you need to get through to reach the Mordavian Valley. The Town of Mordavia section describes the essential places and puzzles in the town proper, and the Valley of Mordavia section does the same for everything outside the town gates.
The above sections briefly describe most of the puzzles which are necessary for beating the game, and the side quests section describes optional quests particular to individual character classes, but may be solvable by anyone depending upon what abilities your hero possess.
The Rescuing Igor section describes a strictly plot related set of events which occurs on day 5 and must be completed to beat the game, and Dealing with Baba Yaga and Rescuing Tanya are two more detailed quests which must be completed after certain events in the game are activated. Obtaining the Rituals is a non linear set of quests which must be completed before EndGame.
Strictly speaking, you could just use all the sections from Rescuing Igor onward as a direct walkthrough to the game. Keep in mind that many puzzles have alternate solutions, and any method of progressing through the game varies by class.