These tags have been bothering me for a while, and in Danbooru thread the discussion just got ignored and never reached any conclusion. So, here are my thoughts:
In my opinion, there should be
a) cave entrance tag, as images from afar with the entrance being visible are tagged with cave as well.
b) implication from both cave entrance & cave interior to cave. Alternatively, keep cave entrance & cave interior & deprecate cave.
As an extra question that I asked in the Danbooru thread as well: Should cases where the location is inside the cave (like cave interior) but you can also see the entrance hole such as post #23550 be tagged with both cave_interior & cave_entrance?