The almogaren (rock-cut sanctuary) of Risco Caído was discovered in 1996 in the Canary island of Gran Canaria. It is a paradigmatic example of a complex where light and shadow effects of an astronomical character have been found within the recent archaeological discoveries of a religious and ritual character in the Canaries. The main artificially excavated camera of the cultural complex Cave 6 takes the form of a cylinder, topped with a dome in the form of paraboloid. In this dome, a 2m long tunnel is excavated by which the light of the Sun penetrates at dawn, from spring to autumn equinoxes. The entering light projects enigmatic images on the western wall of the sanctuary, where numerous pubic triangles (vulvae − the universal symbol of fertility −) are recorded in low relief. Two dots of light of the sun first illuminate the decorated wall in March 19th (and september 25th) in the proleptic Gregorian Calendar, colliding and forming a single image for the time of the equinox, thus allowing the determination of a rough midpoint in time between the solstices. The rising and ascending sun then penetrates the cave during the spring and summer months, reaching its extreme at the moment of the summer solstice when the light takes a form roughly resembling a phallus illuminating the vulvae. This paper will desscribe the site and these series of illuminating effects and will discuss how this could have been interpreted by the ancient inhabitants of the island within the context of a lunar-solar calendar related to the cycle of fertility and permanent regeneration of life.