I know its not September 2018 anymore, but this was taken and processed that month. Our camera club had a weekend outing to a nature resort in the Cederberg mountains. One of the attractions is this waterfall. When the flow is low all of the water falls through a natural hole in the slab, making for an interesting image.
The camera was mounted on the tripod without the legs being extended. I stood outside the "cave" and used a strong lamp to hand paint the interior. I fired the camera using a wireless remote, taking multiple shots in the region of 1/10 th to 1/15 th of a sec at ISO 400, F8, and 18 mm. A few of the shots were then combined in post-processing to produce the final image.
regards - Peter