This is the easiest way to get your four skull trophies.

Go to Avelorn and kill the level 25 troll champ at around the loc 20k, 50k.
Go to Saphery and talk to Maedlaine Bloodwine.
Go to Caledor and go east, across wc bridge and turn left. You will see some dirt between the two waterfalls by the mountain. Click on it and you get a scepter. Click on the scepter and then the mound.
Go to Chaos Wastes and head south to NW Praag. The loc is 16k, 13k. You will kill Calvin Lankdorf. Follow the road south from CW that starts about 20k, 500 he will be on the right side at the loc. If there is a mutated peasant there, then he has been killed recently and you will have to wait.