"I've been researching this lengthy eclipse, and I believe it to be the work of Claw Vipers."

—Drognan

Tainted Sun is the third quest of Act II. It is triggered when a player enters the Lost City, upon which a sudden eclipse occurs, engulfing the land in darkness. After talking to Drognan in Lut Gholein, it becomes clear that this is the work of the Claw Viper clan, and the player is told to end this curse by traveling to the Claw Viper Temple.

The Claw Viper Temple is located in the small Valley of Snakes, which lies adjacent to the Lost City. The Temple itself is filled with Claw Vipers and Salamanders, as well as their undead minions. Players should look for the Tainted Sun Altar, which is hidden on the second level of the Temple. Players will encounter more monsters here, including the Super Unique boss known as Fangskin. After the monsters have been defeated, the Tainted Sun Altar must be shattered, finally restoring the sun to its former glory.

Players should also pick up the Amulet of the Viper, which is the final component needed to restore the Horadric Staff. After the Altar has been destroyed and the sun restored, head back to Lut Gholein and speak to the townsfolk to complete the quest.

Diablo II and Lord of Destruction quests
Diablo II quests
Act I — Den of Evil • Sisters' Burial Grounds • Search for Cain • The Forgotten Tower • Tools of the Trade • Sisters to the Slaughter Act II — Radament's Lair • Horadric Staff • Tainted Sun • Arcane Sanctuary • The Summoner • Seven Tombs Act III — The Golden Bird • Blade of the Old Religion • Khalim's Will • Lam Esen's Tome • Blackened Temple • The Guardian Act IV — Fallen Angel • Hell's Forge • Terror's End
Diablo II: Lord of Destruction quests
Act V — Siege on Harrogath • Rescue on Mount Arreat • Prison of Ice • Betrayal of Harrogath • Rite of Passage • Eve of Destruction