Viking: Battle for Asgard/Collectibles

poop peepeelongboat, on the eastern side (right when facing the beach from Brighthelm).

Niflberg: Darkwater
There are six skulls to be found here to achieve Skull Bagger 1.

Galcliff: Holdenfort
There are six skulls to be found here, however the twelve on the island are required for the first half of the achievement Skull Bagger 2.

Galcliff: Caldberg
There are six skulls to be found here, however the twelve on the island are required for the second half of the achievement Skull Bagger 2.

Isaholm: Thornvik
There are four skulls to be found here to achieve Skull Bagger 3.