The steamship Hohentwiel is a paddle wheel steamer and the former yacht of the King of Wurttemberg Wilhelm II on Bodensee.
Today it's the oldest, still circulating passenger ship on this lake.

David Cronenberg reherse with Michael and Keira Knightley the scene of conversation between Carl Gustav Jung & Sabina Spielrein...

To this young man was offered a role in the film, he shared his impressions of the meeting with Michael:

Julian Laitenberger: "The atmosphere on board was very friendly", describes the young student, especially Michael Fassbender, who behaved absolutely freely. "He has simply joined us at lunch", Julian marvels. Keira Knightley disappeared immediately after each scene below deck and looked more distant. Very unapproachable person, but sometimes Julian was only for a meter away from her."
SZon