Corrupt Well is a Mystery.
Discovery[]
Head west from Everflowing Glade until reaching a broken bridge to the north. There is a nearby stone tile with the seal of Atum on it. Use 
Reveal on it to restore the bridge and unlock the Mystery.
Walkthrough[]
Use 
Purify on the corruption covering the well. The corruption will be dispelled, and an EPIC Arcane Chest will appear. Open the chest to complete the Mystery.