The lowest point in Mammoth Cave?

Answer 1

Not a readily-answerable question beyond Depth of 379 feet, but to me, as a caver I would want to know not only the depth but also what point it is in the entire Mammoth / Flint Ridge system! That's what your question implies. You'd need to study the survey or formal description, written by the cavers who surveyed it, to learn thet.

That's not especially deep, but Mammoth makes up for that in sheer length, the total of known and surveyed passages forming the entire system being somewhere between 350 and 400 miles (depending on source!), making it the world's longest.