I did however decide to add some elements that were not in the original concept, but tried to keep them within the theme and logic of this fantasy world. I replaced the monks in the composition with statues holding candles. I thought that the cave would get very dark at night and would need something to light the path. I added stalactites and extra foliage to closer match my main cave reference, Son Doong Cave from Vietnam, but kept the plants' designs similar to that found in England. I also added subtle story elements like druid carvings and shrines, as well as a pathway up to Camelot on the surface.
This is a time-lapse of the environment in Unreal Engine 4. From initial block out, to final light bake.