This image could be practicle if your are visiting a church on Athos. Where you see Porch (at the entrance) in the Athos churches you will find the Exo-narthex, with in most churches beautiful frescos and stained glas windows. As a non-orthodox visitor in most cases during services you will not get further then the Narthex. After the service you sometimes will be invited to go to the Nave accompanied ofcourse by a father. We got, for instance, a very nice tour in the monastery of Vatopedi where they even showed us the holy relics in the Nave near the Templon. The Sanctuary is a no go area, I think not only, for non-orthodox but for every pelgrim. I found this picture on this blog.