St. Thomas Monastery is a ruined Armenian monastery overlooking Lake Van in Turkey. The monastery is situated near the village of Kanzak (Altinsac), on the Southern shore of Lake Van. It was probably constructed in the 11th to 13th centuries, and is mentioned in manuscripts from the 15th century. Parts of the inside were restored in 1581 and the exterior brickwork was repaired in 1801. It was already deserted before the start of the First World War, with the last monks leaving during the 1895 Hamidian Massacres when the building was attacked by Kurds.