Opening the door in the Staff of Magnus requires a few specific steps. First, you must locate and collect the three pieces of Ancient Nordic Pickaxe scattered throughout Skyrim. Once these have been collected, they must be taken to an obscure location known as Labyrinthian located east of Morthal. Here you will find an entrance guarded by a powerful mage called Morokei who is protected by two Frost Atronachs. After defeating them, you can enter the ruins and search for another door that leads to a chamber containing a pedestal with four slots for placing Runes. You must place all three pieces of Ancient Nordic Pickaxe into these slots which then unlocks the main gate leading to deeper chambers within Labyrinthian where you will finally encounter The Staff Of Magnus locked away behind one more magical barrier that only those bearing its key can open - this is usually obtained from completing certain quests or exploring hidden areas around Skyrim..