The ATM Cave Tour begins with a 45-minute hike through the jungle, leading to three river crossings that may require swimming or using ropes to navigate the current. Water levels are often high, so participants should expect to arrive at the cave entrance fully soaked. After gearing up with helmets and headlamps, the group enters the cave by swimming through its water-filled mouth. Over the next three hours, the tour involves climbing over rocks, swimming through large chambers, and navigating narrow passages—one famously known as “the Headlock.” This journey offers a rare and challenging glimpse into the sacred world of the ancient Maya.

The Actun Tunichil Muknal, conveniently abbreviated as "ATM", was first explored in the late 1980s. The entrance to the cave is shaped like an hour glass and is flooded with water. Remains of ceremonial offerings begin just inside the cave mouth, starting with snail shells and growing stranger and more abundant as one moves deeper into the cave. In the cave’s “Main Chamber,” archaeologists have uncovered the complete remains of 14 individuals—seven adults and seven children, all under the age of five. These were not ceremonial burials, but sacrificial offerings. Among the Maya, purity was deeply symbolic, and young women in particular were seen as "zuhui" — innocent and untouched, qualities believed to be pleasing to the gods. Their lives, given in ritual sacrifice, were meant to ensure balance, fertility, rain, and the favor of powerful, unseen forces that shaped Maya life and death.

Deep within the ATM cave lies one of its most haunting discoveries—the “Crystal Maiden,” long believed to be the remains of an 18-year-old woman, though some scholars now suggest the individual may have been male. This person is thought to have been offered as a sacrifice to the gods of the underworld, a final act of devotion in a sacred space. Over centuries, mineral-rich water flowing through the cave gradually fused the bones to the floor, leaving a shimmering layer of brown calcite that gives the figure its iconic, crystalline appearance.

Over 1,400 artifacts have been uncovered and carefully cataloged, offering a window into the lives and beliefs of the ancient Maya. These include ceramic pottery, water vessels, stone tools, and weapons — many dating from AD 250 to 909, meaning the most recent artifact is over 1,100 years old. Each item was likely placed with purpose, part of sacred rituals meant to communicate with the gods of the underworld. Actun Tunichil Muknal remains one of the most remarkable archaeological cave sites ever discovered, both for the sheer number of artifacts and the story they tell of a civilization deeply connected to the spirit world.