The Osario itself, like El Castillo, is a step-pyramid temple dominating its platform, only on a smaller scale. Like its larger neighbor, it has four sides with staircases on each side. There is a temple on top, but unlike El Castillo, at the center is an opening into the pyramid which leads to a natural cave 12 metres below. Edward H. Thompson excavated this cave in the late 19th century, and because he found several skeletons and artifacts such as jade beads, he named the structure The High Priests' Temple. Archaeologists today believe the structure was neither a tomb nor that the personages buried in it were priests.