Outer end of passage and junction of main and secondary casings.
The gap shown above has presumably be left to shown the outer facing of the
primary casing,
this is the vertical wall face in the centre of the shot partially lit by
sunlight. The secondary casing
was built against this facing and this is the stonework layer seen on the
left above.
The passage is visible lower right, the slight "step" in its walling at about a
metre is the original
location of the edge-set lintels that roofed it, the actual right angle edge of
the passage mouth
is restoration.