Gradierwerk, Graduation tower in Bad Dürkheim, Germany

The Gradierwerk is a 333-metre-long, up to 18-metre-high timber-framed structure in Bad Dürkheim, built between 1847 and 1850. Around 250,000 bundles of brushwood are stacked into walls, and brine from a healing spring trickles over them. The photograph shows dark vertical slats behind pale wooden posts and diagonal braces, with a railed upper walkway and a base of rough reddish and grey stone pillars.

The present tower was built between 1847 and 1850 under saltworks director Albert Schenk, on the site of the earlier Zweybrücken graduation house. Salt was produced until 1913, after which the structure served only for breathing therapy. Arson destroyed sections in 1992 and 2007; it was restored and reopened in 2010.

Locals call the structure simply "Gradierwerk", "Gradierbau" or "Saline". Since 1913, when salt production was abandoned as unprofitable, it has served only for breathing therapy through the salt aerosols released into the air. The spa and saltworks association had run the saltworks since 1872.

The site is open year-round and visitors can walk freely alongside the structure while breathing the salt-laden air. Weather can be damp near the walls due to the flowing water, so dress accordingly when you visit.

The thorn walls are made of roughly 250,000 bundles of brushwood stacked into walls, over which brine from a healing spring trickles; on hot days up to 25 m³ evaporate. The structure was placed under monument protection in 1984. Between 1859 and 1960 it was fed with water from the Alte Maxquelle, which had the highest arsenic content in Germany.