"An Inventory of the Ancient Monuments of Brecknock (Brycheiniog) - Part i: Later Prehistoric Monuments and Unenclosed Settlements to 1000 A.D." Royal Commission on the Ancient and Historical Monuments of Wales (1997)
Absolutely beautiful hardback book, essentially Coflein (for Breconshire) in paper form.
Has comprehensive lists and details for Breconshire's: Cave Archaeology, Upper Palaeolithic and Mesolithic sites, Neolithic Court Tombs, Round Cairns and Barrows of the Bronze Age, Stone Circles and Stone Settings, Standing Stones, Burned Mounds, Unenclosed Settlements, Crannog (and some later things like inscribed stones). Includes lots of "lost" and destroyed sites.
329pp, 9 colour plates and 174 B&W illustrations, plans etc.
100% worth finding a second-hand copy if you're interested in South Wales' prehistory, despite being a few years old.