What exactly was the deep hole?
A slight ledge was over it which Ivy stepped on and it gave way.
It was 10-15 feet deep, almost completely circular, with straight edges. It would take a lot of effort and ingenuity to have been dug manually.
What was it? A trap? A sinkhole?
I think the conceit is that this is "naturally occurring", but I cannot see how such a thing could exist in nature.
If it were caused by water erosion, the hole would not be nearly so circular, and there would be evidence of an entrance and an exit for the water.