Basic Concept: How to build a castle, fort, or keep.
This sourcebook is all about the logistics of castle building and maintaining. If you're running or playing a game that involves any kind of long-term use of a castle, this is a great sourcebook to have on hand. Honestly, it doesn't really matter what system, as the basic building info is based on at least mostly-historical information. That makes this a really solid resource, and I learned a lot about how castles work, how they are built, how they survive/thrive, etc.