An Edge Over Which It Is Impossible To Look
“What we have here,” he adds, “is a geometrical oddity: an edge over which it is impossible to look. Because you can see the endless walls of the abyss both below you and facing you, nothing is hidden except what is down the hole. Standing on the rim, you are very close to a mystery: a space receiving the light of the sun into which we cannot see.”
Regarding the drainage wells found in reservoirs.