During the equinoxes of March and September, sunlight reaches the bottom of the well. Standing in the central part of the staircase, facing south, a peculiar configuration of shadows can be observed. The observer sees his own shadow reflected in the basin containing the water while casting a second shadow, reversed, on the wall of the underground chamber. Two shadows are thereby created, the heads of which touch and create a very evocative phenomenon.
Another phenomenon is the Moon, which is reflected in the basin containing the water through the gap in the tholos. According to some scholars, this phenomenon takes place following a perfect alignment that occurs only every 18 years and 6 months.
