Sonnenstein is a complex and difficult site. The castle itself has a long history: a medieval fortress that controlled the Elbe valley, then a residence, then from 1811 the home of one of the first purpose-built psychiatric hospitals in Germany — a progressive institution under its founding director, Johann Christian Reil, who believed in humane treatment of the mentally ill and was instrumental in establishing psychiatry as a medical discipline.
In 1940, the Nazis requisitioned the hospital and converted part of it into a killing centre under the Aktion T4 programme. Between June 1940 and August 1941, 13,720 people — patients transferred from psychiatric hospitals across Germany and Austria — were murdered here by carbon monoxide gassing. The perpetrators then used the site to experiment with methods that would later be industrialised at the death camps. A memorial, opened in 2000, occupies part of the former killing complex. It includes the preserved cellar where the gas chamber stood, an exhibition on the T4 programme and its victims, and documentation of the individual people killed. The hospital buildings continue to function as a psychiatric facility today, which means the memorial coexists with an active care institution — a deliberate statement about continuity and responsibility.
The memorial is free to visit and open on weekdays. It is not an easy visit, but it is an important one.