One of the most common land snails one encounters in urban areas of western Turkey is Eobania vermiculata, a relatively large, edible species. Presumably, the specific name refers to the vermiculated shell.
It is probably not native to Turkey, but originates from another Mediterranean country. It is so widespread now—as a result of intentional and unintentional introductions by humans—that it is difficult to determine its original range.
In Turkey, Eobania vermiculata is often found with another edible alien, Helix aspersa (or Cantareus aspersus, etc.). One may often see them stuck right next to each other on walls. Obviously, each species has a high tolerance for the other one.
The snail on top is Cantareus aspersus and the one below is Eobania vermiculata. Photo by Deniz.
To the uninitiated, the 2 species may be difficult to tell apart. Here are some pointers to help distinguish them.
Here is a subadult Eobania vermiculata that hasn't yet formed the reflected lip of adult shells.