Tinturn Abbey
Tinturn Abbey is a ruin just barely inside the Welsh border near Cardiff.  Sitting on the west bank of the Wye, it is another Cistercian house founded in 1131.  The church, of the decorated style, was built in 1270-1325.  All that remains are the walls, but that makes it very surreal to walk through.  It's a nice place to visit, and again, not many tourists.