After the dispiriting runaround we had on Day Three, we decide to take our unused tanks and go for a morning deep dive at Sabak Ha, "Dark Water" cenote. Sabak Ha is very open at the surface and resembles a large pond or small, still lake with a coat of lilypads across its top. Below the surface, Sabak Ha is like an inverted bowl, becoming increasingly wider in a series of craggy steps pocked with ledges and small fissures.

The local Maya believe Sabak Ha is bottomless, and to date, no scientist or explorer has been able to prove them wrong. Human divers using special blends of breathing gases have reported achieving depths of almost 500 feet in the cenote, and several ROV missions, including one that assisted Memo on our previous expedition were unable to hit bottom. The top of the debris pile starts at 200 feet.

Sabak Ha is intriguing because of its reputation. Since it's "bottomless," Memo says, the Maya today reason that it's a very dangerous place from which noone comes back. (A diver's life was, in fact, recently lost in Sabak Ha.) Did the ancient Maya also believe that Sabak Ha held the same power? If they did, the cenote may have served some ritual use.

Finding the artifacts to prove this theory will be very difficult with the equipment we have today. We're diving solely on air, and plan to go no deeper than 180 feet, which means we won't even hit the debris pile, the area of the cenote where artifacts are usually deposited. Even if we were to skim the pile, our previous ROV survey revealed it to be a mess of rotting trees, dangerous tangles of fishing line, and a very deep layer of silt with no readily visible artifacts.

We're not even expecting to find anything this morning--this is just one of Memo's favorite sites to dive, an utterly spectacular cenote that will "knock my fins off."

The plan is to drop a stage bottle (a back-up tank) on a 80-foot rope right where we enter the water. We'll follow the rope down, then swim over to the closest wall of the cenote and head down to the cave opening in the side of the wall, the top of which hits at around 170 feet, then work our way back up the wall.

The first 80 feet of the dive is greenish murk--it's hard to see your own outstretched hand--and we huddle around the line to keep each other in sight. At the bottom of the line, however, the murk clears, and Sabak Ha opens up. It's absolutely enormous, and you can see for hundreds of feet.

Although the visibility is extreme, the cenote is so large that you can't see across to the opposite side. It's impossible to even see the debris pile in the center of the site. By the time all of of the divers reach the wall, the stage bottle, with its flashing strobe, looks like a tiny satellite in the empty distance. And of course, there's nothing below us. It's like diving in outer space. It's beautiful, but at the same time it's spooky as hell.

We spread out and start idly nosing in the nooks along the wall. In most cenotes, archaeologists pay careful attention to such nooks and ledges within the first 30-40 feet of the entrance; bodies and artifacts are frequently deposited there. Here, we're poking around at 120, 130 feet because there's nowhere else to look, really. You can turn away from the wall and marvel at the sheer vast emptiness before you, but its so disorienting that noone's about to jaunt off alone in seach of the debris pile.

We swim deeper back under a ledge, then another ledge, then another as the cenote widens in a series of successive steps. Then the cave comes into view. It's enormous; its mouth seems to yawn open like an airplane hangar. If there ever was the perfect entrance to Xibalba, the Maya Underworld, this is it.

The strangest thing about the dive is that we do find some artifacts: Geoff spots a couple pottery sherds in a little nook at a depth of about 160 feet. This is in a wall a good 40, 50 feet back from the cenote opening. How did they get there? What's more, on a ledge maybe ten feet below the sherds, Memo finds the headless, heavily eroded skeleton of a cow-like animal. Again, the body is tucked far back away from the mouth of the cenote.

Little do we know that we'll cross paths with the man who best understands the power of Sabak Ha at our next stop: the local gas station.

After the dive, we head off to a nearby village, where friends of Dionisio suspect they have a cenote that Memo may be interested in. It's late afternoon already, so we decide just to take a quick look at it, and if the site looks reasonable, to come back tomorrow to dive it.

We stop first at the village's gathering point, the gas station, to meet up with Dionisio's buddies, then head out into the fields to check out the site. After what feels like a half-hour hike, we arrive at our destination. It looks like a dry cave, housing a bevy of angry wasps and an even angrier rattlesnake.

Our guides suspect that there are artifacts in the cave, and unsucessfully attempt to trap the rattler so that we can have a closer look. By now the sun is quickly sinking in the sky, and we have a hike ahead of us back to the village. We decide to head back. There's a gracious offer to burn habanero peppers in the cave tomorrow morning to drive out the rattlesnake if we'd like to return for another try. There's also an offer to see the ruins when we get back to the village.

"Ruins?"

"Yes. At our baseball field."

We arrive at the ball field at twilight. Large, wooded hills, about 75 feet high, rise from every side. "Do you know what these are?" Memo says to us, pointing to the hills. "Classic period pyramids. Pyramids centered around a ancient ceremonial plaza. That's why they chose to put the baseball field here. It's nice and flat."

One of the men who accompanied us points to one of the pyramids. "Looters came here, about 15 years ago, and they walked away with two sculptures of jaguars."

"Have government archaeologists ever studied the site?"

"INAH was here about a decade ago," says Memo.

"Sometimes we go to the pyramids but we don't go often and only in the daytime," continues the man. "When I was little, a group of men went to the top of that pyramid there, and went inside a tunnel on the top, and one man never came back."

"Sounds like Sabak Ha," someone comments.

Turns out, the village has a very good shaman who performs the annual cha-chac (rain ceremony) at Sabak Ha. This request for rain is a continuation of the ritual performed by the ancient Maya--although today, of course, it is done without human sacrifice. We ask if we can meet him.

The shaman's house is right near the beginning of the village, at the impromptu gas station. Memo knocks on the door and a small, white-haired man answers. It's the same man who we met filling up trucks earlier in the day. Don Paco listens closely as Memo explains who we are and what we're doing. Then he turns and peers at the scraggly group of tired, dirty divers on his doorstep.

"Yes, I'm the one who performs the cha-chac at Sabak Ha."

Eerily, out of the blue, a very light rain begins to fall.

"I'll explain to you how to protect yourself in cenotes. There are good spirits and there are bad spirits. And I'll pray over you for protection. But not tonight. It's too late. Come tomorrow. But don't come too late then either. OK?" The shaman raises his eyebrows, looking for agreement.

"And bring candles." With that, he shuts his door, and the rain stops.