Malcolm Saville at Clun Castle in 1947

This aerial photograph of Clun Castle was taken in 1947, which was the same year taht Malcolm Saville sent his young heroes there in The Secret of Grey Walls - an exciting story of sheep rustling:

Ten minutes later the Lone Piners passed down Clun's main street towards Castle Hill. The twins, side by side, and in step, led the way with Mackie at their heels. Peter walked between the two boys wile Jenny danced around the party until David complained that she was making him giddy. 

They climbed the hill, trying to guess where the drawbridge would have been when the castle was manned, until they were actually in the shadow of the mighty walls of the keep. 

From here they could look down over the roofs of the little town in one direction, over the river which curled around three sides of the hill in another, and, when they turned right round, they saw the rolling hills and woods which were all that now remained ot Clun Forest, and in the far distance, the gaunt line of the Black Mountains and the other tumbled hilltops over the Welsh border.

Note that Peter was a girl (Petronella) and David could be a bit of a square.