Among natural sanctuaries, the interest of grottoes is that they may be localized and analyzed using literary and iconographical sources as well as through archaeological discoveries. In Greece, approximately 130 grottoes may be identified for the historical periods. This paper is mainly devoted to matters of space : ritual spaces, if any–in and around grottoes–and the role of grottoes themselves as elements of the religious landscape. I argue that grottoes most often had no need of a clearly defined ritual space, all the more so because, due to their location outside of the urban fabric, they rarely hosted community religious activities and were most often visited by isolated pilgrims.