This would have been the entrance/door. The tomb is aligned facing east. The northern portal, almost 2.5 metres tall, still stands, along with the northern side-wall of the chamber. The rest of the stones have collapsed.
The stone in the foreground is the base of the smashed, southern portal. As the capstone collapsed it snapped this stone in two and pushed the top part 2 metres away – you can see that in the background here, its plane matching exactly that of the foreground stone.
All of the structural stones here are vast – the remaining standing portal, the standing side-wall stone, the collapsed (under the capstone) side-wall stone and of course the mighty capstone.