The Stream of Immortality is hidden inside Achamâz. It runs through an underground hospital used during the Creation War (1486 DE - 8777 DE) . The blood of Covenant soldiers, and some angels, mixed with this stream, giving it a powerful blessing.
Water from the Stream of Immortality function as longevity potions. They can also be used to nullify any restrictions that may be in effect versus divine denial of raising the dead; like when Hades is a major power.
Reaching the Stream of Immortality is no easy task. Achamâz is guarded by powerful creatures and laden with defenses to keep out interlopers. Raxcvillibus Dumu-loc claims to have drank from it many times before he became a hell knight. Another said to have drank its mystical waters is Phîn Râlda, founder of the bardic academy at Malêth Sônê.