The Elder Scrolls IV: Oblivion Guide - Main Quest Walkthrough
Blood of the Daedra
Speak to Martin about his progress deciphering the Mysterium Xarxes. He explains that four items are required to open a portal to Camoran's Paradise. So far, he has only managed to identify one of these items, which is the 'Blood of a Daedra Lord.' This, Martin goes on to explain, refers to a Daedric artifact.
In total, there are fourteen different Daedric artifacts in Cyrodiil. Several of these artifacts are incredibly useful items. To obtain one of these artifacts, you first must locate a Daedric Lord's shrine, and then present a specific offering or meet a certain condition. Fulfill the requirements to converse with that Daedric Lord. You will be given a quest; complete this quest to attain the Daedric artifact as a reward.
Reading the 'Modern Heretics' book on Martin's desk will mark the Shrine of Azura on your map. Keep in mind, however, that any one of the fourteen Daedric artifacts are sufficient as a means of opening portal. The artifact received for completing Azura's quest happens to be the incredibly useful Star of Azura, which acts as a reusable Grand Soul Gem. Giving an artifact Martin essentially means destroying it. You won't want to give up the Star of Azura, as it is arguably one of the best items in game.
Give Martin an expendable Daedric artifact, such as Sheogorath's Wabbajack.
Refer to the Daedric Shrine Quests section of this guide for a listing of each and every Daedric Shrine quest. A couple of the Daedric artifacts are not nearly as useful as the others, so look over the rewards as outlined in the Daedric Shrine Quests section of this guide and decide which of the fourteen you would be willing to part with.
The Mace of Molag Bal is a good choice, especially if your character does not use blunt weapons. The problem here, however, is that your character must be at least level seventeen to be accepted by Molag Bal. So, depending on your level, you may not be able acquire the Mace of Molag Bal at this time. Whereas Azura's quest has a level requirement of only two, the reward gained for completing the quest is much too useful to give up.
If your character is below level ten, Sheogorath's reward is a good choice. Complete Sheogorath's quest to receive a weapon called 'Wabbajack' for a reward. The Wabbajack, while a fun weapon, is essentially useless. As with Azura, Sheogorath's level requirement is only two.
Once you have acquired an expendable Daedric artifact, return to Cloud Ruler Temple and hand it over to Martin to complete the quest.