The dark mound in foreground,is the mound of the western defensive ditch to the site.The earthen brown mound in the shade of the trees,is the motte,whilst,out of view,just behind the modern building,is the sudden,50 foot drop into Yr Hafesb(the River Banwy),which runs alongside the site.
see http://www.castlewales.com/mathrafl.html
see http://en.wikipedia.org/wiki/Mathrafal