I'm going to make an entire web page with these explaining what they are, but here's one of me in the bottom of KV-20, Hatshepsut's orginal tomb.
Several things to note: First, the respirator: At the time (1993) the tomb was open, so it was an absolute heaven for bats. The ground next to the walls on the way down is littered with bat skeletons. And, of course, their leavings. So it absolutely reeked. Hence, the breathing apparatus.
Second, it's very long and deep. See this page for a description and plan. And it curves, so once you get to the bottom there is no light at all. This is probably the first time I experienced true lack of light. You open your eyes and there isn't even a smidgen of light. Until you've experienced it, it's hard to explain.
Third, note the very rough walls. The lower half of this tomb was dug into Esna shale which underlies the Theban limestone that most of the Valley of the Kings tombs are dug into. It's very soft and probably nearly impossible to make a straight wall out of. Also, John Rutherford, our geologist/engineer on that trip, had previously mapped the contact between the two formations and it was very nearly flat over several miles. In many spots in the Valley you can see the contact which is usually very distinct.
The Theban limestone is bright white when first exposed, is very fine-grained, and not terribly hard, which made it nice to dig in. It's also chock full o' chert nodules which must have given the builders fits because it's so much harder than the limestone. Faults in the rock also tend to get filed with hard calcite(?) which also gave them trouble, and often you will see blobs of calcite coming out of tomb walls where they quit trying to get it flat (I have some photos of this for later).
Anyway, KV-20 went down into this shale and it's a very rough construction. This may be why it was abandoned(?). Virtually impossible to plaster and paint over, I would guess. I think the builders were aware of this and IIRC knew when to not dig down any further in certain tombs.