Immediately after the end of the Second World War, the castle served as accommodation for “displaced persons” and refugees. In 1948 the castle and its associated agricultural business were handed back to the Upper Austrian State Charitable Association. However, the castle was not returned to its previous use as a care home for people with disabilities.
After the great Danube flood of 1954, the Alkoven local authority accommodated people rendered homeless in the castle. Up to 30 tenants continued to live in the castle afterwards.
In 1968, the Upper Austrian State Charitable Association succeeded in re-establishing the site as a care centre for people with disabilities. The Hartheim Institute was built within sight of the castle. This institution and its parent organisation the State Charitable Association (today: GSI – Gesellschaft für sociale Initiativen [Society for Social Initiatives]), were conscious of their responsibility to commemorate the victims of Nazi euthanasia, and in 1969 constructed the first two memorial rooms in the castle. The Upper Austrian State Charitable Association saw the Hartheim Institute as the “living place of atonement for all victims in Hartheim Castle”.
Over the years the conviction grew that any continued use of the castle as a residential building was incompatible with an awareness of the site’s history. There were a series of approaches and initiatives towards a worthy commemoration in Hartheim Castle, but they all failed. Finally, in 1995, the Hartheim Castle Society was set up. Its aim was for the castle to be solely used as a place of remembrance and exhibitions. In 1997 the State of Upper Austria decided to support this goal and to fund a site of learning and remembrance. In 1999 the remaining tenants of the castle were found other homes and work started on renovating and restoring the castle. After these extensive works to the castle and the outbuildings between 2000 and 2003, Hartheim Castle was opened as a place of learning and remembrance in 2003, housing the memorial and the exhibition “Value of life”.