Sima de los Huesos, Archaeological cave in the Sierra de Atapuerca, Spain

Sima de los Huesos is a fossil-bearing chamber in the Cueva Mayor–Cueva Silo cave complex in the Sierra de Atapuerca, Spain. It lies at the bottom of a vertical shaft, 13 to 14 metres deep, in the corner of the Sala de los Cíclopes. The chamber has yielded more than 6,500 human bone fragments, including a nearly complete skull nicknamed Miguelón.

The bone remains date back approximately 430,000 years and belong to at least 28 different individuals. Genetic studies show a mix of Neanderthal and Denisovan traits in this early population.

The single large Acheulean handaxe found among the bones is the only stone tool in the pit. Its placement with the dead, and the predominance of adolescents and young adults, suggest the bodies were deliberately deposited, possibly as an early ritual act.

The site is closed to the public and entered only by research teams. Access to the bone chamber is through the Cueva Mayor entrance, followed by a walk through the cave system to the 13 m vertical shaft; the chamber lies at its base. The shaft is the only entrance, and sediment is removed in blocks carried out through the cave.

A handaxe from the Acheulean period was found among the bones and is the only stone tool at this location. This discovery suggests the bones were deliberately placed in the shaft, possibly as part of early burial practices.