Diablo II/Forgotten Tower

Unlike the other quests in Act I, this is triggered by an NPC outside the Rogue Encampment and it is an optional quest. To trigger this quest, find the Mouldy Tome in the Stony Field and read it to trigger the quest:

''"...And so it came to pass that the Countess, who once bathed in the rejuvenating blood of a hundred virgins, was burned alive. And her castle in which so many cruel deeds took place fell rapidly to ruin. Rising over the buried dungeons in that god-forsaken wilderness, a solitary tower, like some monument to Evil, is all that remains.

The Countess's fortune was believed to be divided among the clergy, although some say that more remains unfound, still buried alongside the rotting skulls that bear mute witness to the inhumanity of the human creature."

Interesting, now head to the Black Marsh to find the Dark Tower, don't know how to get there? Well it's accessible from Dark Wood if you've done the "Search for Cain" quest. Whilst you're at the Black Marsh, it is recommend to look for the waypoint as well which would prove useful. Once you find the tower (not much of tower since it's collapsed) head into the cellars, your destination is the 5th floor of the cellar. Don't worry too much about navigation since the cellars are relatively small, the only thing you should be worried about here is the Super Unique monster on every floor ranging from undead wraiths to zombies. Once you arrive on the 5th floor, explore around the area and open every chest to obtain mounds of gold, the Countess is located in the back room and oddly, she's a fire enchanted corrupted rogue. Furthermore she is surrounded by her fellow rogues to back her up. Pull out the minor rogues out of the room slowly and kill them before facing the countess. The countess shouldn't be too hard so the fight would be relatively quick. The quest ends as soon as you defeat the Countess.