You can get the Amulet of Slantwig after the Amulet of the North. I stood in front of the throne when I first went through the cave, but not for long enough (I'm pretty sure you don't need any of the 3 amulets from the derelict tunnels, you just need to wait a few seconds with your weapons on your back). Later I returned after Joram mentioned it in a post, which I'm pretty sure was after I completed the derelict tunnels (in D2:ED I got the amulet myself; in DKS I vaguely recalled there being something special about the throne, but was too impatient to figure it out again, so left intending to try again later, then promptly forgot about it, until reminded).
