Includes a water conduit, canal & railway tunnels, gun emplacements on Flat Holm, coal mining & nuclear bunkers:
http://www.bbc.co.uk/iplayer/episode/b08t3qcj/hidden-cardiff-with-will-millard
Mike
http://www.bbc.co.uk/iplayer/episode/b08t3qcj/hidden-cardiff-with-will-millard
Mike