"The Giant and Vigi the Loon: Best Choice"

It seems like missing part when you reach Drove, find Hjalmar, find the skeleton with the note immediately to the left after entering the Drove, loot the village and so on..

"then swim to the south-eastern end of the chamber, where - behind a large stalagmite - you’ll find another chest."

And another one in the most north-eastern corner, behind group of aardable-stalagmite.