What were the chambers like?

Watch the video.

Rerun the video and stop it when you see the gallery and burial chambers.

Now put three desks together end on end and two more tables sticking out from near one end. The plan you make is like a cross.

Place the backs of chairs against the sides to close the tables in.

Now crawl along the gallery made by the tables and see what the three end chambers feel like in terms of size.