Gwyneth's journal is a holotape in the Fallout 4 add-on Far Harbor.
Location[]
The holotape can be found in a house at Kawaketak Station, just east of the Children of Atom shrine, as part of the quest The Heretic.
Transcript[]
Sister Gwyneth: It's done. The messages are posted. I-I know it could mean my life, but the Children must know. I was paging through a pre-war tome when I saw it. The atom. A tiny speck of matter surrounded by endless depths. A vast emptiness that dwells within us all. It only reaffirmed what I'd felt all this time. The truth the Confessor wanted no one to hear. The lie that is Atom. It's not real! We aren't all infinite worlds. Just empty space. Dead. Cold. That we are Nothing. Confessor won't be pleased by my messages, but I'm not afraid. I'm going to start moving things to the old church by the west access road, in case... in case they decide to join me. I-I just hope I'm not too late to save them from Atom's lies.