Cult Curiosity Quest - what cult shrine

[setonix26]

I have to find research notes at a Cult Shrine for the mysterious dagger. I would have thought that the map would point to an island with tall trees and the cult shrine with the red pool and skull in the middle. However it points towards a large island of 2x2 maps squares. Is the cult shrine they refer to in a cave or those smaller cult areas. There is an area with skeletons and some kind of shrine, but no research nots. I've scoured the island 3 times without finding any clue as to where I need to be.
This is a sub quest for the Twisted Blade Quest, a task I need to do for Godfrey.

[setonix26]

I should have written this question earlier. Right after I posted I found some smaller islands half connected to the big island and there was a kind of shrine with 3 cultists and chairs neatly placed next to each other like in church. There I found the research notes.