The way I understood it, you had to book it once you were there in person
There are 2 tours. One is shorter and more vertical changes and one longer and less up and down. We paid when we got there. There is someway to pay online but didn't try to figure it out. We went on the longer walk. Being that have plenty of traction. There is a film of water on the ground in most places. I work new flip-flops and didn't have an issue.
Yoy may book it at the entrance. Its wonderful!
You can book your tour online or at the location.
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