Schloss Hartheim Schloss Hartheim , located at Alkoven in Upper Austria , some 14 km . from Linz , Austria , became notorious as one of the Nazi Euthanasia killing centers , where the killing program Action T4 took place ( see Hartheim Euthanasia Centre ) . The castle was built by Jakob von Aspen in 1600 . It is one of the most important Renaissance castles in Austria . In 1898 , Prince Camillo Heinrich Starhemberg ( 1835 - 1900 ) donated the castle as a gift to the Upper Austria Charity Organization . With the help of additional donations , they used the castle from the beginning of the 20th century as a psychiatric institution ( German : " Psychiatrische Anstalt " , but originally called the " Idioten - Anstalt " ) . History to 1940 . Hartheim lies in the middle of the so - called Eferding Basin , that runs along the River Danube from Ottensheim to Aschach an der Donau . As early as 1130 a family with the name Hartheim is mentioned in the records . They were vassals of the bishops of Passau . In 1287 three brothers , Conrad , Peter and Henry of Hartheim , were named as owners of the castle as part of a barter arrangement with the Wilhering Abbey . In any case by 1323 another family was named as the owners . Until the middle of the 14th century the site consisted mainly of just one tower , subsequently a residence was added and it was surrounded by a small wall with ramparts and ditches . After changing hands several times the castle ended up in the possession of the Aspen family , who probably built the castle into its present shape . At the beginning of the 1690s they had a completely new castle built conforming to perceptions of the ideal Renaissance style with a regular four - winged building with four polygonal corner towers and a higher central tower . In 1799 George Adam , Prince of Starhemberg , purchased the castle . But by 1862 the castle was in a rather poor condition , as a contemporary report describes : " Doors , windows and ovens are entirely missing , . . . and several ceilings must be replaced " . In 1898 Camillo Henry , Prince of Starhemberg , made a present of the castle building , the outbuildings and some land to the Upper Austrian State Welfare Society ( " Oberösterreichischen Landeswohltätigkeitsverein " or " OÖ . LWV " ) . It was intended to use further donation to convert the building into an " Idiot ' s Institute " as it was described at the time . In addition between 1900 and 1910 major renovation and conversion work was carried out to enable the building to be used as a care home for mentally handicapped people . In 1926 a staircase was dismantled and replaced by a bed lift . Nazi era and aftermath . Following Hitler ' s euthanasia decree in 1939 , Hartheim was selected as one of six euthanasia centres in the Reich . Between May 1940 and December 1944 , approximately 18 , 000 people physically and mentally disabled were killed at Schloss Hartheim by gassing and lethal injection as part of the T - 4 Euthanasia Program , named after the infamous Berlin address " Tiergartenstrasse 4 " . These included about twelve thousand prisoners from the Dachau and Mauthausen concentration camps who were sent here to be gassed . The castle was regularly visited by the psychiatrists Karl Brandt , Professor of Psychiatry at Würzburg University , and Werner Heyde . In 1946 , Alice Ricciardi - von Platen , a psychiatrist and psychoanalyst who practised near Linz , Austria , was invited to join the German team observing the so - called Doctors Trial in Nuremberg . The trial was presided over by American judges , who indicted Karl Brandt and 22 others . The 16 who were convicted included Dr . Josef Mengele ; seven were sentenced to death . Her 1948 book , " Die Tötung Geisteskranker in Deutschland " , ( " The killing of the mentally ill in Germany " ) , was judged a scandal by German medical professionals . After World War II , the building was converted into apartments . Beginning in 1969 , the gas chamber was opened to visitors . Hartheim Castle is now a Memorial Site dedicated to the thousands of physically and mentally handicapped persons who were murdered here by the Nazis .