The relationship between petroglyphs and archaeoastronomy has been treated in several ways in the past. In the present study, we examine a particular motif found among the rock carvings in the north-west of the Iberian Peninsula: a large deer with over-sized horns and an unnatural number of tips on each horn. A multidisciplinary approach combining landscape archaeology, comparative history of religions, and archaeoastronomy suggests a coherent interpretation of the motif. It reveals a unique amalgamation of calendrical motives, landscape relationships and lunisolar events. It may also be significant in relation to the Celtic world-view and its artistic manifestation, and to the relationship between time and landscape.