The poster for this movie is very deceiving, and shows a smirking Nora-Jane Noone, who plays Bernadette.
The story takes place in Ireland in the 1960's, but these asylums, which made money by using the residents as free labor in their laundries, had been established in the 18th century. It is horrifying to find out that the last Magdalene Laundry closed in 1996. Also, these places were not relics of fundamental religion in uber-Catholic Ireland either, there was a location in Philadelphia, PA.
So the residents of these places were 'fallen women': aka unwed mothers, girls who were suspected to be promiscuous, girls who had been raped, etc. The nuns tell the girls that hard work and penance will give them salvation and an entrace to Heaven, and they must follow the way of Mary Magdalene.
It certainly sounds unpleasant, but not necessarily horrifying. EXCEPT: these nuns are scary! They have none of the understanding, forgiveness, compassion or gentle humor that characterizes the nuns who taught me in school.
They miss no opportunity to humiliate and hurt the girls. I think the most disturbing scene is one where the girls are in the shower room, anhe nuns play a cruel and perverted game to judge them based on their bodies. (Smallest breasts, biggest bottom, etc)