Nice relaxing 90 min tour up the river to the grotto. Once there walked to it, history and live singing and dancing for us. Nice Hawaiian songs on way back from the guides/staff was a treat.
Leave on the 9:30 trip and get the full music experience all the way up the river. Gotto isn't all that, but cruising up the river is soothing and reminds me of African Queen.
Skip it! We were miserable. They take you in a boat of around 150 people. Six rows, only two of which have a view. So you have a 33% chance of being able to see. The entertainment was awful.