Jörðgarð Book 3 -The Jörð Game Masters Guide (Dungeons Daring RD)

From the introduction: The players' book contains all of the basic information over the campaign setting and its world, known as the jörð. As a game master, you need to know everything in the Players' Guide. This book continues where the Players' Guide ends, containing the information you need to know but that your players aren't allowed to know yet.