Endgame Secrets by Christopher Lutz is definitely a book for more advanced players, perhaps 2100 and above. It consists of 45 games, most of them deeply annotated (6-7 pages is not uncommon towards the end). Lutz is a specialist on rook-and-minor-piece endings, of which there are 20. I used this book briefly with another master, and found it fascinating, although we did find a serious error in one of the games (sorry, but I can't remember which one!). Almost all the principles of endgame play (and many exceptions) are found here, although it takes careful study to absorb them in depth. Ultimately, that is always the case, and I would compare this book to Speelman's brilliant Analyzing the Endgame and Endgame Preparation.