There are probably nicer things to do on a Sunday than to spend it in the dark prison cells of a former Stasi prison, but a visit to Gedenkstätte Hohenschönhausen is worth it anyways. Not only do you learn a ton, you can also find out beforehand whether a contemporary witness will be giving the tour, adding many personal impressions to the historical facts. In addition you'll be extremely thankful to be free to roam after a two hour tour of one of the darkest chapters of GDR history.