These prisoners ("Sonder- oder Ehrenhäftlinge", "special or honorable detainees") included political leaders from Nazi-occupied Europe and disgraced members of the German elite.
[1] The Nazi regime classified its political prisoners into numerous categories, including The latter category also included the "personal prisoners of the Führer" – opponents of the Nazi regime too prominent to be killed outright, as well as people like Hitler's failed assassin Georg Elser, who was initially kept alive with the intention of putting him on a show trial after the war.
[1] As the war wore on, the SS increasingly requisitioned a great number of hotels, castles, palaces and mansions, and repurposed them as detention centers.
Albert Speer was charged to rebuild the Schwarzburg castle in the Schwarzatal, Thuringia, for this purpose, but the project was eventually abandoned.
In 1942, the SS decided to use the Pakri Islands near Baltischport (now Paldiski in Estonia) for this purpose, but German defeat at the Battle of Stalingrad put this position at risk and the project was also abandoned.