This article deals with an almost unknown group of Christian monuments, churches, that is, housed in caves.

The reasons for their creation are explained as well as the way of their construction and the traditional inclinations and mentality of their builders.

Three such churches are described. The rock sheltered church of St. Christodoulos in the Limni of Euboea, dating back to 1102 ΑD and that of St. Nicolas in Skyros Island, dating before 1806 AD. The cavernous church of St. Athanasios the Athonite in Skyros, that dates back to 1602, is also presented.