Derek Brockway visits the Elan Valley in Powys, for a stunning seven-mile circular walk punctuated by dams. He learns how the valley was flooded to supply water to Birmingham, has a go a mountain biking and discovers the part the area played in the Dambusters attack. Dr Erin Lloyd Jones visit the ruins of the ancient abbey at Strata Florida and Jonny Cotsen meets military veterans who have taken up art