A graduation works or tower, also known as a thorn house, is a construction used to produce salt by evaporation of water. The tower consists of a wall-like frame stuffed with bundles of brushwood. The water, from a local river or well runs down the tower and partly evaporates, thus concentrating the salt content while undesired minerals precipitate on the twigs. The twigs have to be replaced about every 5 to 10 years. Graduation towers are notably found in spa resorts in eastern Europe, primarily in Germany. They are now more of a tourist attraction than a viable industrial practice. Photographed in Bad Munster, Germany.