Back to Hollow Knight
The Fog Canyon can be found early on but it’s difficult to navigate without the Shade Cloak and Isma’s Tear. You can access it from all sides. For this walkthrough I’ll assume you’re coming from the lower side of the Fungal Wastes at the very bottom of the map.
If you follow the passage to the left you’ll find Millibelle the Banker. You can open an account for 100 Geo and store your Geo there for safe-keeping.
Heading up the tall cavern the passage mid-way up to the left leads to the Queen’s Gardens. Continue up to the top and take the exit to the left. About half-way up this next cavern, to the left, is a passage that leads to the Overgrown Mound. Along the way take the exit to the top for a Lifeblood Cocoon and Hallownest Seal.
In the Overgrown Mound fight your way past the Squits and pick up the Howling Wraiths spell. You can find the upgrade to this spell, the Abyss Shriek, in the Abyss.
Make your way back to the tall cavern and then take the exit to the right. You’ll need the Shade Cloak to dash past the Shade Gate. Take the exit above to find Cornifer who will sell you a map of the area.
Drop back down and continue to the left. Head up and then through a secret passage to the left. This is a fairly difficult area with exploding jellyfish, Ooma, and exploding eggs. If you can get through them you’ll be rewarded with another Charm Notch.
Now make your way down and back around to the left to the Teacher’s Archives. Before dropping down to the entrance to the Teacher’s Archives super dash across to find a hidden Grub.
Jump up the two platforms to the Bench above. Now might be a good time to change your charms in preparation for the boss fight with Uumuu. This will be a long battle so I chose the Lifeblood Heart and Lifeblood Core as my charms.
Make your way down the Teacher’s Archives to the arena. When you stand on the lowest platform Uumuu will rise up from the pool of acid.
Uumuu only has 300 health but he’s invulnerable while he has his jellyfish armour around him. Quirrel will join you for this battle and every know and again will pop Uumuu’s armour, giving you a chance to damage him. Try to get in as many hits or spells as possible while the armour is popped.
Uumuu has two main attacks, Lightning Burst and Lightning Chase. For the Lightning Burst Uumuu will fill the arena with lightning. There will be safe places to stand but predicting where they will be is difficult as the lightning seems to be random. The Lightning Chase will follow you around the arena for around 6 seconds. You’ll need to keep moving or be damaged by the lightning.
Once Uumuu has been defeated you’ll be free to explore the rest of the teacher’s archives. Find the large tube with the Dreamer inside. Jump up to the top and inspect the button on the left side. After Quirrel has a chat with you use the Dream Nail to hit the tube with the dreamer inside. Head over to the right and kill the Dreamer.
That’s all for this area. If you want to see the True Ending you’ll need to head back and defeat the Dream Bosses for the extra Essence.