Act 1 Quest 4: The Forgotten Tower - Diablo 2
Quest Location: The Forgotten Tower
Quest NPC: The Moldy Tome
Quest Goal: Defeat The Countess
You can pick up this quest by inspecting The Moldy Tome which is found in Stony Field or by entering The Forgotten Tower which is found in Black Marsh. All you have to do for this quest is travel down all 5 levels of The Forgotten Tower and defeat The Countess on the bottom floor.
The final boss of this dungeon, The Countess, has a 100% chance to drop a High Rune as well as a good chance to drop additional High Runes (up to 6). Obviously her dropping 6 High Runes will be extremely rare, but it isn't uncommon for her to drop two or three. For this reason many people farm her early on in Nightmare difficulty to outfit themselves with the best Rune Words they can get their hands on. For more information about this I recommend you check out my Countess Farming Location.
After you defeat The Countess a chest in the back room will open up and start spitting out gold and items everywhere. It's not as good as a super chest but it's better than a regular chest. This chest is technically your 'reward' for beating The Countess as it'll only open when you're on the quest and you complete it.
If you are farming The Countess solely for her High Runes you'll want to skip every thing in the Forgotten Tower as well as all the trash you can skip around The Countess. Maximizing how quickly you can kill The Countess and start a new game is all that will matter since all you're interested in from farming her is the High Runes.
The Countess only dropping one Shael Rune.