Derek and the team travel to 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. On his way round he has a go a mountain biking and discovers the part the area played in the daring Dambusters attack in WW2. Meanwhile archaeologist Dr Erin Lloyd Jones visit the ruins of the ancient abbey at Strata Florida and performer Jonny Cotsen meets military veterans who are being inspired and helped through art.