Very interesting and set in the back drop of the WW2 U-Boat repair pens in Keroman.
Probably the easiest submarine walk-through museum for those with difficulty getting about - there are stairs in and out of the submarine but it is not so restricted inside as you would expect.
English audio tours are available.
Try and go when it's quiet so you can spend more time taking it in without having to jump out of the way of people who are simply rushing through.
Tip - you can purchase this ticket as part of a package with the rest of the attractions in the Base de Sous Marins area