In the lower left of center of the image is an “orange” opening, this is where Warren’s Shaft descends vertically down to a spot near the Gihon Spring.
Notice in the upper right side of the image the line where the lower rock ends. On the left side of the image the same rock formation is visible.
Note too the modern metal staircase that leads up to another portion of the diagonal shaft—that was thoroughly cleared and explored by Ronny Reich.
Reich’s theory is that during the Middle Bronze II Period (ca. 1800 B.C.), and during most of the life of this water system, the whole lower three fourths of this image was SOLID ROCK and that “Warren’s Shaft” was totally unknown.! He maintains that an ancient would have been walking in the upper portion of this image into the continuation of the tunnel that is visible at the top of the metal stairs. Everything from the top of the metal stairs down was SOLID ROCK!
It wasn’t until much later, during the Israelite period that this area was “excavated” and Warren’s Shaft was discovered.
It is not clear why anyone would have wanted to “excavate” this area and subsequently accidentally discover Warren’s Shaft. In my opinion is one of the major weaknesses of Reich’s theory.
The Diagonal Tunnel leads down, from within the ancient city, to a pool that was fed by the Gihon Spring, from which water was drawn. It evidently dates back to the Middle Bronze II Age (= ca. 1800 B.C.) and was used for many centuries.
For a presentation of Reich's theory, see Reich, Ronny, and Shukron, Eli. "Light at the End of the Tunnel: Warren's Shaft Theory of David's Conquests Shattered." Biblical Archaeology Review, vol. 25, no. 1 (January/February, 1999):22–33, 72.