Before the entrance, the large rock hampers easy access to the tomb, indicating the difficulty of crossing the threshold into the spirit world. Above the entrance is a roof box which allows a ray of sunlight to travel along the passage and penetrate the darkness of the tomb every winter solstice on 21 December. The winter solstice, being the shortest day of the year, represents the renewal of life, and the ray of sunlight may represent the sun impregnating the tomb, which is also a womb. Thus people exit the tomb reborn, along the passage that, in its restricted space, may represent the birth canal.
However, the tomb/womb may also represent the human mind, illuminated by the light of consciousness - the darkness representing death (one aspect of the spirit world). The geometric designs in and around and outside the tomb (not just spiral but also triangles and others) are, indeed, most probably the entoptic shapes that people experience in altered states of consciousness. Thus, the Neolithic sites may represent not just a spiritual journey but the discovery of consciousness too, following the tradition of Paleolithic cave art.
Lewis-Williams, D. 2002. The Mind in the Cave: Consciousness and the Origins of Art. London: Thames & Hudson, Ltd.
Lewis-Williams, D and Pearce, D. 2005. Inside the Neolithic Mind: Consciousness, Cosmos and the Realm of the Gods. London: Thames & Hudson Ltd.