No special access issues
The GPS coordinated are in the correct position. Driving/biking from trondheim, before you arrive at the designated parking, there is a open part in the forest on your left. You can walk up here, follow the path left to some concrete construction. From here you can bush through the forest and find Skarpeggen etc. If you continue bushing leftwards maintaining roughly the same elevation you will find hjørnesteinen. Alternatively there is a path in the forest that you can see on the map here. Going from trollaish. This path continues straight to hjørnesteinen.