Hyakuhachi Yagura Tombs are artificial caves on a rock cliff in Kamakura，carved mainly in the 13th - 15th centuries．Their walls are generally dry but one cave exceptionally has distinct vegetation on the walls．The cave is located on a hollowed slope where rainwater is easily gathered．Measurement in this study revealed that when heavy rain （more than 30 mm）is observed：1. water drops are observed from the ceiling near theentrance of the cave，2. the dropped water goes into the cave，3. water content of the floor increeces, and 4. water surface appears and the level goes up．The water brought in this way influences the vegetation．Accordingly，establishment of some drainage system above the cave will be necessary to prevent the water drops from entering the cave to eventually reduce the vegetation
