I'm a tall guy, and started feeling claustrophobic when I saw what some of the tunnel entrances looked like. I never used the measurement tool to verify, but they looked like they'd have made me prefer crawling instead of crouching.
Something that confirmed my suspicion: In the King's chamber, 'stand' next to the sarcophagus, and look behind you. I won't explain further.
I am not normally claustrophobic, but being tall and some of these shafts are very low, I would be unlikely to make it very far before abandoning the attempt. I am glad I saw this though, I can at least do it remotely.
How anyone did this originally and to rob the place, is amazing.
Something that confirmed my suspicion: In the King's chamber, 'stand' next to the sarcophagus, and look behind you. I won't explain further.