The Poidsear Coast plays home to a few of the final acts' main quest and side missions. This is technically a story-related, unmissable trophy, to be honest.

Just head south when you can, which is after “Niamh Fitzgerald’s Trial” and before the “In the Shadow of the Mountain” main quest and you'll get this trophy. These are very late in the day quests - 35 and 36 out of 40, to be precise - so don’t worry too much about when and whether you’ll get access. It’ll come… eventually.