The Elder Scrolls IV: Oblivion Guide - Daedric Shrine Quests
Location: Travel east along the Gold Road leaving Skingrad until the shrine appears on your compass.
Requires: 500 Gold
Level Requirement: Level 20
Reward: Masque of Clavicus Vile
To find Clavicus Vile's Shrine, travel east along the Gold Road leaving Skingrad until the Daedric Shrine symbol appears on your compass. At this point, stray from the road and follow the symbol on your compass. It's quite a ways out, but just keep following the road and it will appear eventually. When you reach the shrine, locate and speak to Ma'Raska. He tells you to leave an offering of 500 gold coins to summon Clavicus Vile. You character must be at least level 20 to begin start this quest.
Leave 500 gold coins to the Shrine of Clavicus Vile to summon the Daedric Prince.
If you have at least 500 gold coins, approach Clavicus Vile's Shrine and offer them to summon the Daedric Prince. Clavicus Vile wants you to find a warrior named Umbra, kill her, and retrieve the Umbra sword. He points you to the Pell's Gate settlement, where you are to begin your search. Barbas, Clavicus Vile's hound, will be added to your inventory in the form of a statuette. He tries to convince you that you've made a bad deal, and urges you not to give Umbra to Clavicus. Either way, if you want to complete this quest, you'll have to defeat Umbra and retrieve her sword, even if you don't intend to hand it over to Clavicus.
If you ask Irroke the Wide at Pell's Gate about Umbra, he'll tell you about the sword and the person. Umbra is in the ruins of Vindasel, which is located just southwest of the Imperial City. Travel west along the road from Pell's Gate and you will soon come to Vindasel.
Enter Vindasel and follow the arrow on your compass to find Umbra. Umbra, unlike every other enemy in Oblivion, is not level scaled. This means that her level is static, as she does not level along with your character. At level 50, she is quite powerful; depending on your level, you may have a tough time defeating her. She is equipped with a full set of Ebony armour and is wielding the Umbra sword, which is the strongest sword in the game (sans Shivering Isles).
Find Umbra in Vindasel, defeat her, and bring her Umbra sword back to Clavicus Vile's Shrine.
Barbas will again attempt to convince you to forget about Clavicus' wishes, but you will need to defeat Umbra if you want to complete this quest. If you have a strong enchanted weapon and plenty of Health potions, you should be able to take down Umbra without too much difficulty. When she is dead, remove the Umbra sword (and her Ebony armour if you wish) and exit Vindasel. Return to Clavicus Vile's Shrine with the sword in hand. Once at the shrine, you can either give the Umbra sword to Clavicus, or keep it for yourself.
Umbra has the highest damage output of any sword in the game (sans Shivering Isles), and in its current state, is weightless. If you decide to keep the sword for yourself, however, it will then weigh 45 pounds. The sword does have the ever-useful Soul Trap on Strike enchantment, which works nicely when used in conjunction with Azura's Star.
If you give Umbra to Clavicus Vile, he will reward you with the Masque of Clavicus, which is a helmet that will raise your character's Personality attribute while equipped. If you want authorial advice, keep the sword, as it is much more useful than Clavicus' artifact. Even if you don't give him the sword, the game will still count this Daedric quest as complete.