From the back cover:
Inside this sourcebook, you will find details on the history of castles, the construction of castles, the folk who dwell in and around castles, as well as how castles age to become ruins.
In Castles & Ruins you get:
Many new Training Packages that represent the covations and lifestyles of the folk around castles.
A new kind of spell list in Rolemaster: Training Package Spell Lists. These spell lists only become available through training packages.
Details on the processes used in castle construction (finding sites, materials, labor, etc.). Guidelines on costs are also provided.
Details on staffing of castles as well as notes about the day-to-day operations of these bastions of power.
Guidelines on how castles age, becoming ruins. These ruins and other structures are often the sites of lost treasure and many adventures.
From Guild Companion release:
Originally published in 1996 by ICE, this new edition of Castles and Ruins has been digitally remastered by The Guild Companion.
Castles and Ruins is a sourcebook dealing with the details of castles, construction of dwellings, and the aging of ruins. Designed for use with the Rolemaster Standard System and wholly compatible with Rolemaster Fantasy Role-Play.