You are in fact quite close to the end after 'Revealing the Unseen'. It's time to end this and restore peace to Winterhold. Note that you can still perform radiant, side and spell-master quests after you complete the main story.
Containment*** Spoiler - click to reveal ***Ancano's actions have caused casualties among the Mages and has put Winterhold into jeopardy as it is now overrun by magical anomalies. Destroy such abnormalities and return to Mirabelle, who will give you an item that will allow you entrance to the Labyrinthian. So off you go, to get the Staff of Magnus.
The Staff of Magnus*** Spoiler - click to reveal ***The Labyrinthian is a substantial dungeon, with some effective enemies inside, so I advise you don't go if you are of low level. Upon entering the Labyrinthian you will witness reminisciences of the past; get used to it as you will have many sequences with the mage ghosts as you crawl along the dungeon. At first you will encounter mostly skeletons in the corridors, which are not much of a threat. The real deal begins once you cross the timed door (you'll probably need to use the Whirlwind Sprint Shout) as a Skeletal Dragon is waiting for you. Fight it as you would any dragon, except it won't fly (I don't know whether that's because its skinless or the encounter occurs indoors) and you will have a horde of unpleased undead coming at you. You can take a lot of damage quickly if you're not careful. Here I recommend using any Undead perking ability you have (weapon, spell, items...) to get rid of the minions, then go at the dragon. When cleared, go deeper unto the Labyrinthian Chasm.
There is little worthy of notice through the chasm, except for a voice you will hear here and there that will drain your magicka. You will cross plenty of Draugr Wraiths, Atronachs and rune traps so be on the look-out. There is even a Whispmother at some point in the Thoroughfare. You will eventually make it to the tribune, where you will find a shout word and further on Morokei imprisoned by two enthralled wizards. You have to free the Dragon Priest by disintegrating its guards and then fight it to the end. Morokai uses principally shock attacks, so anything you have that protects you from that magic will come in handy. Once beaten, you can proceed out of the dungeon, fight a final enemy and go back to Winterhold.
The Eye of Magnus*** Spoiler - click to reveal ***Upon returning to the College, you will find it is caught in a maelstrom of magic caused by Ancano. Use the Staff to make it through to the Hall of Elements, where you will face Ancano. He will start by casting a paralysis spell, leaving you to stand alone against him. What you have to do is to use the Staff on the Eye to close it; as long as it is open Ancano is invulnerable to damage. He also runs a lot around, so using a bow will prove helpful to hit Ancano. If the Eye reopens, some anomalies will come out and you will have to close the Eye again to pursue inflicting damage to Ancano. Eventually you will defeat him, but the Eye will remain active. Quaranir appears again and takes away the Eye with the help of a few brethren. Tolfdir will now name you Arch-Mage of the College. Congratulations for your promotion
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