Mainly we wanted to see some of the church sites in the old city (aka Upper City, Ano Polis), as they themselves are -- well -- very old. We got off the bus right at the Monastery of Vlatades. Unfortunately, we got there around 2:30, so no one was around and the buildings were locked (afternoon rest time). But we did get to walk around the monastery. It turns out the Patriarchal Institute for Patristic Studies is attached to the monastery.
Now when we got off the bus, there was a sign for this monastery (which was actually only about 10 feet away from the sign) and another sign for the Temple of Osios David (Righteous David, King and Prophet), which was originally part of the Monastery of Latomou. (BTW, I finally got an answer on why some saints are called Righteous as opposed to just Saint -- as in this, case "Osios" means "Righteous." It turns out that traditionally only monks and martyrs are called Agios or Saint.) Anyway, the signs were right next to each other, and both pointed in the same direction.
These photos of Thessaloniki were taken from near Trigonion Tower.