We present archaeoastronomical results of an interdisciplinary project to study Bronze Age sites of the socalled Cultura de las Motillas in the Spanish region of La Mancha. We find that winter solstice sunrise was of special importance in the funerary  and perhaps religious  practises of these peoples. The impressive megalithic monumental complex of Castillejo del Bonete shows a remarkable marker of the winter solstice sunrise on the most peculiar mountain of its horizon as well as alignments with this and other singular solar events as equinox and summer solstice. There seems to be a correspondence between the orientations of some of the main architectural structures of the monument and the general arrangement of two of the main galleries of a natural cave that lies just beneath it. Markers and orientations to the winter solstice sunrise seem to be present in other nearby contemporary sites such as the necropolis of Cerro Ortega and the motilla of El Azuer. Castillejo del Bonete stands as the first evidence of a clear solar marker in a megalithic site of the Iberian Peninsula, indicating that the precise location of the monument was carefully chosen. The alignments defined by several of its structures further reinforce its astronomical symbolism.