The wilds of Skyrim have many mystical and magical dungeons to explore, though none are as mysterious as those explored during the College of Winterhold questline. In particular, the Labyrinthian, explored while searching for the Staff of Magnus, is one of the most mysterious dungeons you can explore, both in relation to the College's storyline as well as the rest of Skyrim's history.
Not only are there several enemies inside the Labyrinthan that aren't seen anywhere else, but there is also a lot of items and gear that can only be found inside that are useful for just about every kind of character you might want to build.
Enemies
Immediately surrounding the Labyrinthian are several Frost Trolls that can be easily dispatched with some well-placed Fire spells or knocking them around with melee attacks. One enemy you should be wary about, however, is the dragon that is perched atop the mountain that looks over the area, as it can sometimes swoop down at the worst possible moment and join the fight.
Inside the Labyrinthian, the first enemies you will come across are multiple Skeletons, but the strangest enemy is the skeletal dragon that lays in the middle of the room. Unlike other dragons, this one won't grow its skin back and doesn't appear to have been reanimated by Alduin, instead being animated by some other force inside the dungeon. You will also encounter spectral Draugr that wield unique ghostly Nordic weapons, though the real test of strength comes at the end of the dungeon.
After reaching the final room, you will have to face off against Morokei, a Dragon Priest wielding the Staff of Magnus alongside some destructive spells. This fight can quickly turn in Morokei's favor if they are allowed to use the Staff of Magnus too much, especially if you are playing as a mage, so keeping your distance is the best way to deal with this particular Dragon Priest.
Loot
Even for a Dragon Priest dungeon, there is a significant amount of loot to be found inside the Labyrinthian. Outside the dungeon, there is a small hut containing the Wooden Mask that, when combined with every other Dragon Priest mask in the game, will allow you to obtain Konahrik, a unique mask that has a chance to instantly heal you when at low health while also dealing a large amount of damage to nearby enemies. When combined with the Avoid Death Restoration Perk, it is possible to always be able to avoid dying, even in the hardest battles. There is also a Pickpocket skill book, Aevar Stone-Singer, in the same area as the Konahrik mask.
Once inside the dungeon, there are several possible Spell Tomes that can be found, as well as one unique tome that can't be found anywhere else. On the righthand side of the first chamber in the Labyrinthian, you can find either Ironflesh, Detect Life, Waterbreathing, or Telekinesis on a table. In the room with the arcane enchanter, you can find the Spell Tome for Equilibrium, which damages your health to regenerate Magicka, as well as the Immortal Blood book that documents Morvath's past before becoming a vampire.
The spectral Nordic weapons, the Drainblood Battleaxe, Drainheart Sword, and Drainspell Bow are unique weapons that drain health, stamina, and Magicka respectfully and are only found inside the Labyrinthian. You can acquire multiples of all of these weapons as well as disenchant them to learn their effects, which is particularly helpful for the Drainblood Battleaxe since it, for some reason, is counted as a separate Drain Health enchantment from every other Drain Health enchantment and can be stacked if you have the Extra Effect perk.
There is also a unique Ancient Nordic Helm, the Ancient Helmet of the Unburned, found being a locked gate in Labyrinthian Tribune alongside a Honed Ancient Nordic Greatsword of Scorching and an Ebony Shield. In the final room where Morokei is found, you can obtain the Staff of Magnus, which is necessary for the continuation of the College of Winterhold questline, as well as the Dragon Priest mask Morokei, a Light Armor headpiece that increases Magicka regeneration by 100%.
Quests
For the entire area, there are only two quests that involve the Labyrinthian or its immediate surroundings: The Staff of Magnus, which is the only way to get inside the Labyrinthian, and the unnamed quest which involves completing Shalidor's Maze in order to be rewarded with the Diadem of the Savant, a unique crown that reduces the cost of all magic by 5%. The Staff of Magnus can be started immediately after Containment and Savos Aren's death once Ancano decides to start messing with the Eye of Magnus for his own gain.
Shalidor's Maze can be completed at any time and is accessed directly east of Bromjunaar Sanctuary, where you can find the Wooden Mask. Traversing this maze can be difficult for multiple reasons, as it is designed to trip you up while exploring it, though the hardest aspect comes when you have to battle Dremora and should be attempted when you are comfortable battling high-level enemies.
Secrets
The biggest secrets that the Labyrinthian holds are in its exterior rather than inside the dungeon itself. That being said, this area is the only one in the game that holds multiple different Word Walls. A Word Wall for Dismay, which acts like a Fear spell, is found inside Shalidor's Maze, while a Word Wall for Slow Time can be found in Morokei's room inside the Labyrinthian.
There is also something of a bug in Morokei's room, as the enthralled mages that protect him aren't who they should be. After Savos Aren abandons his companions, Atmah and Hafnar Ice-Fist, they are imprisoned by Morokei, but when you reach his room, both of the mages are male despite Atmah being female.