1. I assume you mean the iron door? Its opened by pulling a lever in the prison, but that lever is protected by a teleporter that takes you to an identical lever, thus tricking you (maybe) into thinking you've pulled the first one, hit that second lever to disable the teleport on the first lever
2.That key is for an area beyond the relay room
3.Glacial fragment is an ice element agent for the spell forge
4. Ok spell forge, heres how you do it, first get two correct items , you have 2 x legionary shield recipe so place one shield each in the reciever and agent terminal, now activate the forge by hitting the receptor for that class (in this case the armor receptor) with a fireball (theres a fireball staff hidden in the forge if you don't have Clave/he can't cast fireball). This will cause a new item to appear on the altar
This recipe is fairly basic, but others will require you to know the difference between the agent and reciever, The reciever is the item to get enchanted the agent the item providing the enchantment. For example the glacial fragment will give ice magic to an item (if it capable) eg. a spear, this would enchanted via the weapon reciever
if thats not clear try this
https://www.youtube.com/watch?v=Lpj3ebTMh1w I made this video to help anyone who is lost as to how the spell forge works
5. Alot of people are having trouble with this room, its a timing puzzle, one plate fires a shot that travels a short distance the other a longer distance, throw an item onto the long plate (there are some shuriken in the room) then run and stand on the short plate, A third shot will fire at the receptor near the door block it and the door will open.
As I said others have had trouble here, my testers made it through easy, but if you still have trouble let me know and I'll loosen the timing to make it easier
6.The human remains are a clue for the "once for each of the eastern dead" button in the cells hitting the button the correct number of times opens a secret door, they also can be used at the forge if you find the recipe