The Well of Sorrows, or vir'abelasan, is an ancient nexus of ley energies located within the Temple of Mythal.
Corypheus began searching the Arbor Wilds for elven artifacts. Morrigan assumes that he was searching for an eluvian to physically enter the Fade, but when she and the Inquisitor overhear him talk about the Well of Sorrows, it makes them doubt that the eluvian is the darkspawn's true goal.
The leader of the temple's guardians, Abelas, attempts to destroy the Well to prevent it from being desecrated by outsiders. If the Inquisitor had allied with Abelas earlier, he can be convinced to relent and allow access to the Well, though he warns that doing so will come with a price: whoever drinks from the Well will gain the knowledge of the previous servants of Mythal, but be bound to the will of the elven goddess.
Morrigan identifies the Well as the "key" to the resident eluvian and partaking from it will render it useless to Corypheus. She makes no secret of her desire to drink from it, believing that she is the most qualified to preserve its knowledge. Either Morrigan or the Inquisitor can drink from the Well. Soon after, Corypheus forces his way into the Temple and glides to attack. The Inquisitor's party retreats through the eluvian back to Skyhold as the water from the Well rises up with an unknown feminine figure inside it, blocking Corypheus' way. As soon as the Inquisitor makes it through the mirror, the figure crashes into the eluvian, which is destroyed upon being touched by Corypheus.
Whoever drank from the Well begins to hear the voices of Mythal's servants, who reveal that Corypheus' Red Lyrium Dragon is the key to defeating him; by killing the dragon, it will disrupt Corypheus' ability to leap into other bodies, rendering him vulnerable.When the Inquisitor and Morrigan later encounter Flemeth, the voices from the Well reveal that she is the vessel of Mythal and whoever drank from the Well can be controlled at her whim.