The best time to shoot the waterfall is early in the morning - that way it's possible to have them all to oneself, rather than jostling for tripod position with other tourists.
The waterfall is not the only point of interest in the cave. Glow worms occur here naturally, although sadly their number is falling. When too exposed to too much light, such as a camera flash, a chemical reaction occurs within the glow worm causing it to basically burn to death. Unfortunately too many tourists don't heed the warnings and they are slowly disappearing. As they don't move around much it's quite possible to get bonus shots of them using long exposures and the tripod while it's set up for the waterfall.
In order to get this photo I left home at 3:30am and drove nonstop arriving just before sunrise. Slipping and sliding down the wet rainforest path was all worthwhile to find myself alone with this lovely scene. I highly recommend the effort to anyone living close enough to experience the same.