What’s that under the Great Pyramid?

On the Megalithic Marvels of Egypt tour we were privileged to receive a 2 hour long after-hours visit inside the Great Pyramid of Giza. Upon entering the descending passage, our first big stop was to visit the subterranean chamber - the basement of the Great Pyramid! I was taken back by how long and steep this passage leading down underneath the pyramid was (approx 300+ ft). While the higher passageways & chambers were lined and finished with precision megalithic blocks, the passage leading down was unfinished in that it was cut straight from the bedrock. Once we reached the bottom, the passageway leveled out & we had to literally crawl on our hands and knees through thick pyramid dust the final section (approx 10 yards) before entering the subterranean chamber. This chamber seemed essentially like a big square with 3 levels - the upper level with smallish cutouts or storage type areas, the main level which featured this circular fence, which in turn, sealed us off from the lower level which is a massive pit with a squared out bottom that featured what appeared to be a nubbed circle popping up in the center of it. What do you think the purpose of this pit was? I will share my theories in more videos coming soon… on the far side of the main level was another tight passageway that led to another smallish room.