I have started the "Under Saarthal" quest and once I remove the amulet from the door and get trapped, it does not show up in my inventory. I have re-loaded several times with no luck. In one case I even reloaded to the start of entering the quest and then went off and completed other quests and sold stuff etc. but when I returned to the quest, the same issue occurred at the exact same point. Again, I have reloaded but to no avail. I have confirmed that I am not looking for the wrong item, it is simply not in my inventory. This issue is preventing me from progressing the Mage's and Forbidden Legend questlines. Any ideas?
This seems to be a bug in Skyrim. If you're on PC I would recommend you download the "Unofficial Skyrim Patch" as it fixes a lot of these bugs.
Again, if you're on PC you can add the item to your inventory by typing:
This should add the amulet to your inv, and the quest should go on as usual! :)