An Indonesian spelunker named Hamrullah was exploring the grounds of a concrete plant on the island of Sulawesi in 2017 when he spotted the unassuming hole in the limestone high above his head. Without a second thought, he shimmied up the rock and tucked himself into the mouth of a small cave, where he clambered through the tunnel’s cool, musty air. He hit the back wall and saw a mural spread out across eight feet of flaking rock, so he pulled out his phone and began snapping pictures.

The painting, described today in the journal Nature, depicts two pigs and four small-bodied relatives of water buffalo, as well as what appear to be eight humanoid figures that are two