A cenote in Yucatan. The dive guide says that once you go down, you can only hold his hand. – intro video

You are an underwater archaeologist searching for ancient Maya pottery in Yucatan. This cenote is said to connect to a cave river that no one has ever reached the end of. There is only one guide on the entire peninsula willing to take you down, and he has just one condition: "Once we go down, you may only hold my hand. ... If you let go even once, we come back up, and I won't refund your money."