Jesse Eisenberg wrote the role of British tour guide and historian, James, for his friend, actor, writer and director Richard Ayoade. Ayoade thought he would have been a bad fit for the role and his presence would have been too distracting for a serious drama like this so he suggested Eisenberg offer it to Will Sharpe instead.
The hat bought by Benji is a traditional Polish highlander (Gorale) hat. It is worn by men living in the mountains in southern Poland.
The piano pieces heard throughout the film are the work of Frédéric Chopin, a Polish composer and piano virtuoso, who is regarded as one of the greatest musicians in history.
Jennifer Grey, who is Jewish-American, was overwhelmed on visiting Majdanek and couldn't stop crying. Jesse Eisenberg initially kept some of her reaction in the film, but ultimately decided it "disrupted" the tone.