On the walls of the upper façade is a network of abstract shapes. One of these that is prominent throughout is a pair of circles joined together by overarching curves. This is known to be a symbol of the planet Venus. The two dots are suspected of representing the Morning and Evening Star aspects of Venus.
The doorway of the structure appears to have been used as a place to observe Venus. Every eight years, the Morning Star would rise at its farthest position to the south, directly facing the doorway, with accuracy to one-thirtieth of a degree (two minutes).
Also at the Nunnery, the symbol of Venus appears above the doorway. There are X-shaped pieces framed between serpent bars. There is a group of thirty of these pieces in one place, the same number as the days of some lunar months. All the other X-shaped pieces number 584, the average number of days of the orbit of Venus arounf the Sun.