How do you get in the big room in the arch mage tower in oblivion?

To access the big room in the Arch Mage's Tower in "The Elder Scrolls IV: Oblivion," you need to complete the "Recommendation" quests for all the Mages Guild recommendation. After earning the title of Arch Mage, you'll receive the key to the tower, which allows you to enter the big room where various magical resources and items are located. Additionally, the room is accessible once you have completed the main Mages Guild questline.