Le Silence des repentis

The isolation adds so much atmosphere to the story, but I'm curious if the author based it on a personal place or a fictional creation. How did that environment influence the characters' choices?

The tension built up nicely, but there was a stretch where it felt a bit slower. Was that intentional to deepen the characters or suspense?

The suspense kept me guessing, but I wonder if the storytelling choice to drip-feed information was planned from the start or evolved during writing.