The more I look at that logo, the more I like it...
The individual elements fit together in terms of their spacing and sizes, with the smoothness of the font offset by the jagged, irregular edges of the opening. The image itself is great - it's something human scale but alluring; we can tell something is ahead but we don't know what. It belies the usual myth of tiny cave passages, while not trying to show something very large in something very small (which would fail, I think). Whoever and wherever the mysterious figure is (for the general public who won't know), the bag suggests adventure!
I still think it might be a bit complicated; would be worth seeing what it looks like at lower resolution and, where appropriate, in versions without the 'British Caving Association' bit and possibly with a simplified version of the cave passage.