A massive novel and an Epic Volume, The Keep by F. Paul Wilson starts strong and gets better and better. The book has corpses, castles, Nazis, medieval evil and terror hardened villagers and soldiers.  There are mysterious messages written in blood, an unknown evil wreaking havoc, and an ancient sorceror from the 'First Age' of humans.

There's something satisfying about Nazis getting it in the neck.  It's not hard to pinpoint, and the physical and psionic assaults on the hapless German soldiers stasy satisfying til the end.