Castell Odo is an iron age hillfort in Wales. It sits on the summit of a hill and is surrounded by two ramparts.
http://maps.google.com/maps?f=q&hl=en&q=52.822557N,+4.692131W&ll=52.822631,-4.689531&spn=0.023029,0.086517&t=k&om=1
http://www.gtj.org.uk/en/blowup1/1225