Graduation towers of Ciechocinek, Brine graduation towers in Ciechocinek, Poland

The graduation towers of Ciechocinek are three timber brine-evaporation structures built on about 7,000 oak piles driven into the ground. Each stands 15.8 metres high above a 9-metre-wide, 1-metre-deep trough, with spruce-and-pine frames packed with blackthorn over which brine trickles. Towers I and II run parallel, 648 and 719 metres long; tower III, 333 metres, closes the horseshoe from the north.

Work on the first two towers started in 1824 under the direction of Professor Jakub Graff from the Mining Academy in Kielce. The third tower was added later to complete the complex.

The towers form a natural inhalatorium: brine trickles down blackthorn branches and evaporates in wind and sun, releasing iodine, sodium, chlorine and bromine into the air. The complex, with the Tężniowy and Zdrojowy parks, was entered on Poland's list of Historic Monuments in 2017.

The site is open daily, though visiting hours change with the seasons. Visitors should wear comfortable shoes, as the ground around the towers can be wet and slippery from the dripping brine.

More than 7000 oak piles were driven deep into the ground to support the weight of the pine and spruce frames filled with blackthorn. This foundation method was chosen to keep the heavy structures stable over many decades.