We got there late (5 mins to closing time) the last tour leaves an hour before closing so we had very little expectations of seeing anything. We went in and spoke to the rangers who really went out there way to help us.
One of them arranged for us to be taken down and see the caverns from the main entrance. We didnt get to see it all but we got to see the expanse of the main chamber (which is huge) and got some amazing photos. Also we were the only ones down there, it was so peaceful.
We were so impressed with the cavern and the staff, we were just sad not to be able to go on a tour as we had to move out of the area that night.
My advice is get there early and chat to the rangers, they are helpful and informative.
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