Crusader Castles of the Teutonic Knights (1): The red-brick castles of Prussia 1230–1466 by Stephen Turnbull
My rating: 4 of 5 stars
This book provides a solid overview of the Northern European variety of castles along with plenty of the accompanying history (especially for someone whose knowledge of the history of these lands is very poor!) to get decently acquainted.
I would specifically recommend this before anyone planned a trip into Northern Poland or Lithuania, just in case there was something to swing by near the ideal route. The book ends with quite a few recommendations on what to visit, and the photography included throughout is pretty instructive as well.
