An extensive strategy guide for A Plunge into Darkness! Includes:

• annotated maps
  
• a complete walkthrough
  
• general hints and tips
  
• monster weaknesses and battle strategies

How to find the guide

From your computer, go to:
C:\Program Files (x86)\Steam\steamapps\common
Then select the game folder.

Or directly from the Steam Client, first right-click on the game, then select:
Properties > Local Files > Browse Local Files