Sac Actun turns out to be just one section of the world's largest underwater cave. Nido Huebl/Shutterstock

Imagine discovering a site where the remains of a giant sloth sit next to burnt human bones, wall etchings, and a shrine to the Mayan god of war and commerce. That’s exactly what happened to archaeologists exploring an underwater cave in Mexico’s Yucatan peninsula.

Just last month, divers from the Great Maya Aquifer Project came across a passage connecting two underwater caves – the Sac Actun and Dos Ojos networks, revealing that the two are, in fact, interconnected and making it the largest underwater cave in the world.

Wall-to-wall, the cave is roughly 247 kilometers (216 miles) long.

"This immense cave represents the most important submerged archaeological site in the world, as it has more than a hundred archaeological contexts," Guillermo de Anda, an underwater archaeologist with a specialism in Maya civilization, said in a statement last month.

"Along this system, we had documented evidence of the first settlers of America, as well as extinct fauna and, of course, the Mayan culture."

The team presented their findings at a press conference on Monday. Among their discoveries were the skeletal remains of giant sloths, bears, and an animal called a gomphothere. These bizarre, elephant-like creatures had four tusks and dominated the American landscape for millions of years. Sadly, they were driven to extinction during the Pleistocene epoch (2.6 million to 11,700 years ago) through a combination of climate change, the arrival of specialist feeders, and, most probably, humans, who thought prehistoric elephant meat made for a tasty snack.

The archaeologists also found evidence of more recent activity. Several human relics were left behind in the cave, including burnt human bones, wall etchings, and ceramics. The team discovered a shrine to Ek Chuaj, the Mayan god of war and commerce and a staircase that could be accessed through a sinkhole in the jungle.

Mexico's National Institute of Anthropology and History (INAH) told the audience, caves – especially those that led to water – were “extremely sacred places” in ancient Mayan civilizations.

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The team believes that water levels in the cave have fluctuated over the years and that, in times of drought, it provided an important source of water for people and animals living nearby. Accessing the cave could be dangerous and not everyone who entered made it out again, which although unfortunate, has made it an archaeological treasure trove.

"It is very unlikely that there is another site in the world with these characteristics,” de Anda explained in a recent statement.

“There is an impressive amount of archaeological artefacts inside, and the level of preservation is also impressive."