A young group of teens stood on top of a rocky ledge, some fearful, some excited, some just egging their friends to jump. Their trepidations were warranted — it’s not every day you’re faced with a drop of about 30 feet above the surface of a pool of water. But inevitably, each brave adolescent took the leap and gasped for a few seconds of unnerving airtime before gravity plunged them into the cool freshwater below. They joyously celebrated their jumps with smiles and cheers, unbeknownst to them that a whole underworld was beneath their fluttering bare feet. Here, at Cenote Zapote in Quintana Roo, Mexico, lies a netherworld I can only describe as an aquatic version of the Upside Down, the dark, parallel dimension from Netflix’s popular sci-fi series, Stranger Things.
On any given hot tropical day in the Riviera Maya, tourists and locals alike often switch it up from the beach and head inland on the Ruta de los Cenotes, to see and experience the local geological marvels of cenotes — groundwater-filled sinkholes — and enjoy a swim in the jungle. There are hundreds of swim-accessible cenotes across the Yucatán Peninsula, but Cenote Zapote stands apart, not just for its high rocky ledges but for its paleontological and geological history and its enigmatic phenomena within. The only way I could dive deeper and investigate its subterranean mystery was to, quite literally, dive deeper with scuba equipment.
An Upside Down Journey
There are dozens of scuba-accessible cenotes across the Yucután, with many being entry points to vast underwater tunnel networks. Cenote Zapote, on the other hand, is a solitary, hourglass-shaped cavern in Cenotes Zapote Ecopark, about 29 km (18 mi) west of popular beach resort destination Puerto Morelos. Its total depth is about 55 m (180 ft), but even as a PADI-certified advanced diver, I would be limited to roughly 30 m (98.4 ft), which is still quite deep considering that’s about 10 stories down a dark pit of water.
Local dive shops have guides who know the cenotes back and forth, so they are the best way to get down there. Guiding me was Hector Martínez, a freelance dive guide at The Fives Dive Center, based out of The Fives Oceanfront Hotel in Puerto Morelos. We sunk and swam downwards — sometimes straight down in an upside-down position — leaving the sights of swimmers’ treading legs just under the surface. The rippling rays of sunlight from above gradually faded and dimmed as we descended to the point where it only provided a dull, ambient illumination that made everything look like it was in green-tinted, underwater night vision.
The liquid within Cenote Zapote can be divided into three layers. An upper layer of freshwater, sourced from rain, lies atop two prehistoric layers: a murky layer of trapped hydrogen sulfide at about 35 m (115 ft) deep, above a layer of deep saltwater. The debris of the sinkhole’s collapse still lingers, causing small particles to float around, much like in Stranger Things’ parallel dimension. In the center of the pit, jutting out of the cloudy layer of hydrogen sulfide, lies dead fallen trees that appear upright, as if growing from the depths of the unknown. As a scuba diver in this ghastly underwater environment, I felt as if I was slowly sinking down towards an ominous, supernatural world.
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Hellish Formations
Martínez and I descended slowly to about 29 m (95 ft), where we leveled off to swim laterally to explore the big, mysterious discovery of Cenote Zapote — peculiar rock formations known as Hell’s Bells. These phenomena protrude down, like bell-shaped stalactites, from the ceiling of the lower part of the cavern’s hourglass shape. We swam amidst them in darkness because light does not reach underneath the lower ceiling. Using underwater flashlights, we carefully maneuvered between them and shined a light on their magnificence.
Named after the AC/DC song, Hell’s Bells have intrigued scientists so much that a whole international team of speleologists, geologists, paleontologists and microbiologists have assembled to research them, mostly by the University of Heidelberg in Germany. However, at the Mexican forefront is local paleontologist Jerónimo Avilés Olguín Segovia, whose curiosity spearheaded the initial investigation after seeing them during an exploration of a prehistoric sloth at the bottom of the cenote. Discovered by his colleague Vincente Fito in 2011, these conical rock formations do exist in other cenotes, but not at such a size, with individual lengths upwards of 2 m (6 ft) and widths at almost 1 m (3 ft). While in the family of speleothems — which includes stalactites and stalagmites — they’re so unique that they’ve spawned the introduction of a new subtype: redoxithem.
While speleothems are typically formed over time in open air through the dripping and hardening of calcified water, what’s baffling is how the redoxithems have grown within a liquid state — and at a relatively faster rate than their terrestrial relatives. It’s theorized that their growth isn’t geological but rather biological, instigated by the unique combination of different microorganisms within the prehistoric water. However, research and observation is still less than 20 years old, too young for a definitive conclusion.
In Too Deep
With my tank’s air supply rapidly decreasing with the increased pressure of being down so deep, we wrapped up our time with Hell’s Bells and swam back to the center of the hourglass, where the tree trunks and branches rise out of the eerie layer of hydrogen sulfide. I was near my depth limit, circling around the trees to get some footage with my GoPro, only for my buoyancy to sink me a tad deeper, down into the cloud of trapped gas. While I was only in the thick, obscuring fog for a couple of seconds, I felt like I was in a limbo of two dimensions, and I quickly swam upwards to escape any possibility of being stranded in the other one.
Martínez and I carefully ascended up the cenote in a slow and gradual manner to prevent decompression sickness. We took an extended safety stop at around 5 m (15 ft), finally back in the realm of the shimmering sunrays shining from above and the cycling legs of swimmers dangling over us.
I was thrilled to finally be back on land, not only to have returned safely, but because I’d just survived what felt like an almost supernatural experience. Ten stories underwater, it was unlike anywhere else in our world — or our dimension, for that matter.
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