The inter-apse doorway.
The construction here is very similar to
the corresponding doorway in Temple 2 and features two
"slab altars" (the recumbent slabs either side of the portal),
although it lacks the two outer "calendar" slabs.
The flanking slab far left bears a carving of a temple on its inner face, and
this area is illuminated by
the rays of the rising midwinter solstice sun shining through the porthole
doorway.