If this is the point where there are several rock outcrops that you can use
as cover from the bunkers as you make your way along the beach, you should
be able to move up a path between either the first and second or second and
third bunkers. When you come round leftwards at the top of the path to the
back of a bunker, there's a stepped depression in the ground (3 concentric
circles), and behind that a manmade tunnel entrance. Go through the tunnels.
They're not blocked off.