I have done this as well, it was fun. The tunnels make up a small part of it, and only lasts for a few minutes. It is dark as well, but the current and other people around will help you to feel safe. There really are no dangers aside form human error and taking risks. the day that I went was a cooler day and the water was chilly. Other than that, I would do it again. I think you should try it, if you get uncomfortable in the cave, it will be over in a moment and you are not alone.