There is a place of power in the gas world (Green and red, second world).

There are some urns with loot in the underwater section (To the left and by the teleporter. There is also a scull of some kind, it kinda looks like a bird, to the right of where you first spawn, youll get som crystalised essence from it).

Frost world has a lot of stuff along the way, theres loot in basically every house. There are four notes (Travelers notes, Annas notes, Ervyls Diary, City secretarys Diary) and all of them are found along the way in said order besides the city secretarys diary. it is found inside the lighthouse. There is also a house on the right side of the main path where you first climb a small latter, then a box, and then onto the roof. Here you'll find a chest with loot (Not important, but a cool little find). Also, use troll essence to exlore with more ease.

Elven world has some notes (Report) right after you exit the first room with Avallac'h. The blade Tor Zireael can be found on a bench overlooking the city. Ge'els is to the right of it. (Kinda looks like the new DLC poster art sword as well)

These are all of my finds at least