Some of the unique landforms, the so-called ''fairy chimneys'', which were formed within the Cappadocian tuff of central Turkey, were used as dwellings in the past and contain culturally valuable wall paintings. However, these structures are undergoing chemical and physical deterioration due to atmospheric effects. For conservation studies, an understanding of the engineering geological properties of the tuff is essential. In this study, emphasis is placed on both material and mass properties of the tuff. These properties are evaluated for the assessment of rock durability. This study shows that the Cappadocian tuff is almost fresh, with local discoloration, is moderately weak to very weak. and has low unit weight, very high porosity, and high deformability. Discontinuity surveys revealed two dominant joint sets, which not only controlled the formation but also control the structural stability of the fairy chimneys. Various methods used for the durability assessment of the Cappadocian tuff indicate poor to very poor durability. Due consideration must be given to strength reduction due to moisture, poor to very poor durability, and the adverse effects of joints on the structural stability of the fairy chimneys. (C) 1997 Elsevier Science B.V.