Between 1978 and 1983, the Archaeological Department of Sri Lanka conducted systematic excavations at Belilena, uncovering cultural deposits spanning from 30,000 to 9,000 years before present. The layers yielded bone tools, evidence of controlled fire use, and geometric microlithic stone tools whose precision at 30,000 years of age is remarkable by any global standard. Paul E. P. Deraniyagala first discovered the skeletal remains of ten individuals at the site, attributing them to Balangoda Man, a Late Pleistocene population designated Homo sapiens balangodensis. These were not people passing through. The depth and richness of the cultural deposits indicate sustained occupation over millennia, a community that knew this cave intimately and returned to it across hundreds of generations.

The animal bones in Belilena's sediments compose a menu of the prehistoric Sri Lankan diet. Sambar deer and wild boar provided large game. Indian muntjac, several species of monkey, and porcupines supplemented the protein. Indian giant squirrels were hunted from the forest canopy. Reptiles and fish from nearby streams rounded out the fare, along with aquatic and tree snails that were prominent enough in the deposits to suggest they were a dietary staple rather than an occasional addition. Plant remains tell the rest of the story: wild breadfruit and kekuna nuts indicate that Balangoda Man combined hunting with systematic foraging, processing these foods using techniques that would sustain communities for thousands of years before agriculture arrived on the island.

Perhaps the most striking discovery at Belilena is the evidence of long-distance trade. By 30,000 years ago, the cave's inhabitants had established a salt trade network with communities living in coastal lagoons approximately 80 kilometers away. This is not casual exchange between neighboring groups. Eighty kilometers of mountainous, forested terrain separates Belilena from the coast, implying established routes, repeated journeys, and relationships maintained across distance and time. Even more remarkable are the rubble foundations dated to 16,000 years before present, which constitute the earliest evidence of substantial built structures anywhere in South Asia. Before the great civilizations of the Indus Valley or the Ganges Plain laid their first bricks, people at Belilena were constructing shelters with stone foundations inside their cave.

The skeletal fossils recovered from 16,000-year-old sediments were analyzed by an international team of anthropologists, contributing significantly to the understanding of Balangoda Man's physical characteristics and their relationship to other Late Pleistocene populations across South and Southeast Asia. Belilena has since been declared an Archaeological Reserve under Sri Lanka's Antiquities Ordinance, recognizing both its past contributions and its future potential. That unexplored passage beyond the underground lake haunts the imagination. The accessible portions of the cave have already yielded 30,000 years of human history, the oldest known structures on the subcontinent, and evidence of trade networks that predate cities by tens of thousands of years. The cave near Kitulgala guards its deeper secrets behind water, waiting for future archaeologists with technologies that do not yet exist to find out what lies beyond.