“Rainwater that flows into cenotes or seeps in through cracks feeds the river. The water level must be very high after a rain—maybe even through the rainy season—and then gets lower as time passes.”
“Sounds right,” she said. “It would explain why the Mayans built those big stone strips like gutters, to catch the rain and direct it to the pool.”
“When there’s no rain for a while, much of the underground river probably gets low, and air flows in above it. When the river rises again, air gets trapped in places like this,” Sam said. “We’ve got to try to stay on the surface as long as we can to save our air.”
“And by the way,” said Remi, “don’t make any more moves like trying to give me your air tank. I’m already aware that chivalry isn’t dead.”
“I was just being rational,” he said. “You use less air than I do, so you could make it last longer and get farther.”
“All that would accomplish is that we’d both die alone. I plan to die in front of an audience and I picked mine years ago. You’re it.”
“Saves you having to send out a lot of invitations,” he said.
“That’s right,” she said. “This is hard enough with you alive. Just stick with me and curb your generosity.”
They swam on along the curving tunnel for an hour until they came to a spot where the wall ahead reached all the way down under the water. They sto
pped and held on to the wall long enough for an awkward kiss. Then they lowered their masks over their faces and turned on the valves of their tanks. Remi said, “Remember, it’s both of us or neither,” and put her mouthpiece in.
They sank, and found themselves in a long passage that looked exactly like the stretches they had first passed through. As they swam, Remi wished she had looked at her watch before they had submerged. She had timed their arrival at the air pocket at sixteen minutes, but how much time had gone by? And did their tanks actually hold nine more minutes of air? She and Sam had never tested the limits before. Letting their air get this low would have been risky and stupid on any day when they could have simply surfaced and gotten fresh tanks from the dive boat.
There was nothing she could do but swim. As the minutes ticked away, the passage opened into another, wider space. The bottom of the river was oddly uneven, with loose chunks of rock instead of the smooth-worn riverbed they’d seen before. Then she realized she was seeing these things outside the perimeter of their flashlight beams—real light was filtering down from above. They swam upward. As the light grew brighter, Remi laughed and heard herself make a squeaky noise like a dolphin. She saw Sam huff out a big flurry of bubbles in an answering laugh, and they broke the surface smiling.
But Remi’s laugh caught in her throat. There was light in this dome, directly above their heads, coming from a circular hole that opened to the starry sky. But the hole was at the center of the dome, beyond their reach, at least six feet above the surface of the river.
“Now, there’s a problem,” Sam said.
“What can we do?”
“I’m going down to take a look around. Stay here for a minute.” He lowered his mask again and submerged. Remi waited until he surfaced again.
“Well?” she said.
Sam swam over to the side of the stone riverbed. It seemed to rise in the water, then rose partway out of it, so he was only up to his waist. “I’m standing on a pile of rock. At some point, a pretty big chunk of wall came down right here. There’s also a pile in the center, right below where the roof collapsed.”
“Very dramatic,” she said. “Does this mean we’re not going to the great beyond?”
Sam looked up at the hole in the dome. “I think it does, but we’ll have to work pretty hard to get out. Get ready to move some stones.”
They dove to the bottom, where Sam had been standing, and began to move chunks of stone from the pile along the wall to the spot just below the opening. Sam moved the largest chunks he could, rolling them end over end, to add to the pile in the center. Soon he took off his fins and worked in his booties. It was clear that at some point part of the wall had collapsed to make the pile, and stones gradually falling from the ceiling formed the cenote, with even more stones coming down as it enlarged. Sam and Remi both were free diving and they had to stop occasionally to catch their breaths.
When they had moved the whole pile of stone from the place where it had fallen to the place they wanted it, they stopped at the surface. “We’re running out of stones,” said Remi.
“I think we’ve got to bet the rest of our air on finding more and building higher.”
“I’m for risking it,” she said. “This is the only chance we’re likely to get.”
They put on their tanks again, swam in a wider radius around the pile they’d built, and brought back chunks of limestone that must have been left by other collapses. They didn’t bother to pile the rocks high, just brought them and then went back for more, knowing the air in their tanks must be nearly gone. After a few more minutes, Sam surfaced and took off his tank. Within a short time, Remi surfaced too and took off hers.
“All out?” asked Sam.
She nodded.
“All right. Let me arrange what we’ve got as well as I can.” Sam ducked under the water and moved a large stone and added it to the pile. Remi went under and did the same. Each time they submerged, they held their breath and moved one stone before they came up for air. It was a slow and exhausting process, and their rest periods grew longer, but, little by little, the pile rose nearly to the surface. Sam even built their empty tanks into the pile to add height.
Finally, after hours of work, Sam sat down for a moment. “Okay.”
“Okay what?”