The bailey ditch.The bailey rampart is on the rhs.Obviously,over the last thousand years,weathering has somewhat filled in the ditches and levelled the earthen ramparts,but the line of the ditch is still apparent,looking straight into the picture,into the shaded area under the trees,rounding behind the trees to the rhs.
see http://www.castleuk.net/castle_lists_midlands/166/wymondley.htm
see http://www.british-history.ac.uk/report.aspx?compid=43600
http://www.castlefacts.info/castledetails/castleDetails3.aspx?uin=11566
see http://www.hertsdirect.org/libsleisure/heritage1/archaeology/moreaboutarch/archsites/wymondleymotte/