We may have found it! https://youtu.be/yyPMltDjTFw
Apparently there is one last secret / easter egg in the Witcher 3, somewhere in the Crookback bog, in the village with the crones.

The part where the devs talk about it is towards the end of this stream: https://www.twitch.tv/videos/1537361573
Shorter clip can be found on my discord.

My video about Vivienne's secret: https://www.youtube.com/watch?v=NZZ9p1HbeHs

My "Witcher Details" playlist: https://www.youtube.com/playli....st?list=PLMpNwDjXWh0

0:00 One Last Secret in the Witcher 3.
0:32 What the developer hinted at.
1:09 What I understood.
1:22 Which village are they talking about?
1:41 What I think the secret is about.
2:30 What other secrets we know of in the area.
3:06 Ciri, Imlerith, Keira Metz?
3:30 Last crone in the good endings?
3:55 Hail, be praised!

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