Can pay there, if you pay online it has to be paid on the day you are going....so may as well just pay when you get there
Both the options are available.
You can pay online but also when you arrive, check out the flashlight tour "hidden passages". No crawling around the cave but I found that it gave me more of a cave exploration feel and you see parts of the caverns that arent in the standard tour.
You can pay there
You can pay once you get there. Ordering online secures you a spot though incase they have a larger tour...
Pay onsite is fine.
You can pay when you get there.
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