Cain tells you to never forget that your ultimate purpose here in Kurast is to destroy Mephisto. The ancient Horadrim imprisoned the Lord of Hatred inside the Guardian Tower that is located within the Temple City of Travincal.

The only way to gain entry to Mephisto's prison is to destroy the artifact known as the Compelling Orb. Mephisto used this device to control the Zakarum Priests and their followers. The Orb can only be destroyed with an ancient flail imbued with the spirit of the one incorruptible priest.

Your task is to collect the scattered relics of Khalim - his Heart, his Brain, and his Eye. Then, using the Horadric Cube, transmute Khalim's Flail with his relics. Once this is accomplished, you must destroy the Compelling Orb with Khalim's Will to open the way into the corrupt sanctum of Mephisto.

Given by Cain after completing the Golden Bird quest or by entering the Great Marsh.

Tip: The Eye is in Spider Cavern. The Heart is in the Sewers. The Brain is in Flayer Dungeon. The Flail is dropped by one of the High Council members.