At head of title: Cadw: Welsh Historic Monuments.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
A guide to ancient and historic Wales : Dyfed by Sian E. Rees. ISBN 0117012203. Published by H.M.S.O. in 1992. Publication and catalogue information, links to buy online and reader comments.
obnb.uk is a Good Stuff website.