Yesterday, I got this book from one of my players (also GM in our Pathfinder game and the designer of said book).
It is an occult history book by the fictive Dr. Cagliostro – investigator of the unknown. Although not a game book per se, this book oozes of cool inspiration for your Call of Cthulhu or Ravenloft games.In fact, it is very much in the style of Van Richten books from Ravenloft. You will find cool stories, steampunk style artefacts (locally built by the author I think) and general gothic feel within the pages of this book.
Good news are that although the book is written and produced in Sweden, it is in English, so you don’t have to take Swedish class to get to it’s goodies.
Here is a web page with more info: