The depression at bottom left looks exactly like an old mine shaft, whereas the hole further back looks to be natural. It may just be a bit of artistic license, 'compiling' features not that far away - maybe he tried painting one of the swallets in its actual location and didn't like it, so he 'moved' it. Given there are no trees around it though, it seems unlikely to be a swallet, more of a collapse. Judging by his painting style, absolute realism wasn't his primary aim. It's very psychedelic in style - I'd like to see more of his work.
One of the old paintings we used in The Castleton Mines book showed a view of Peak Cavern Gorge from the village, relatively denuded of trees, and it shows a large opening 'somewhere' around the base of the slope that now holds the access path to Peveril Castle. Despite numerous long stares I've never been able to figure out where it could be - but then figured that the artist had probably just dragged one of the nearby Cave Dale caves 'around the corner' to make it fit, despite it breaking the rules of physics and optics - but you can do that in painting, unlike photography.
