Most of the joints between the blocks of the walls run perpendicular to the floor, with two exceptions. Firstly, those in the lower third of the corridor are vertical. Secondly, the three girdle stones that are inserted near the middle (about 10 cubits apart) presumably stabilize the tunnel.[150]

Well Shaft and Grotto
Grotto (left) accessed through the broken wall of the Well Shaft (right)
The Well Shaft (also known as the Service Shaft or Vertical Shaft) links the lower end of the Grand Gallery to the bottom of the Descending Passage, about 50 metres (160 ft) further down.
It takes a winding and indirect course. The upper half goes through the nucleus masonry of the pyramid. It runs vertical at first for 8 metres (26 ft), then slightly angles southwards for about the same distance, until it hits bedrock approximately 5.7 metres (19 ft) above the pyramid's base level. Another vertical section descends further, which is partially lined with masonry that has been broken through to a cavity known as the Grotto. 