Osterstein is the former castle keep of Zwickau. First mentioned as Castrum Czwickaw, it was damaged in a fire that ravaged the town in 1403. Demolished and reconstructed, it was subsequently converted to a stately Renaissance residence between 1587 and 1590. From 1775 to 1962, it served as a correctional institute.
After it was decommissioned in this role, the historical building was abandoned to decay. Extensive work took place between 2006 and 2008 to restore the home of the royal Wettin family to its former glory. Perhaps the most famous guest was Martin Luther who delivered a sermon at the castle on 2nd May 1522. August Bebel and Karl May served prison sentences here.