Interesting interpretation of the challenge; nice to see something different (I did one of the interminable train-track shots).
I think the lighting lets you down pretty seriously here, and ends up leaving a pretty snapshottish effect; it's just pretty flat - I can't tell if you used on-camera flash or (I suspect) natural lighting but either way it's from directly behind you, so you lose the texture. The dramatic cave shots I think of tend to have several lights hidden in the foreground to accentuate the shapes in the cave.