Blood of the Divines - The Elder Scrolls IV: Oblivion
After giving Martin some time to figure out the next item needed to open a portal to Cameron's Paradise, speak to him to learn of the second item on the list, the blood of a Divine. Though Martin is unable to discern what exactly this refers to, Jauffre is able to figure it out, so speak to him. He'll tell you that the Armor of Tiber Septim, a holy relic of the Blades, would be adequate. The armour, Jauffre explains, is buried deep within the catacombs of Sancre Tor, to which he provides you a key.
Sancre Tor is located west of Bruma; Jauffre has marked the location on your map. It is a relatively long trek to Sancre Tor, so to make things easier on yourself, be sure to set 'Blood of the Divines' as your active quest. This way, you can simply follow the active quest marker on your compass. Alternatively, if you have discovered any locations on the map that are near Sancre Tor, you can fast travel there to shorten the journey. Otherwise, Weynon Priory might make a good starting point.
Once there, walk along the walls of the fort and locate the entrance. Be careful, as there is likely some variation of skeleton warrior beyond the walls. You'll encounter a multitude of undead creatures in the catacombs of Sancre Tor. Depending on your character's level, you may or may not encounter ghosts. Be sure to bring along a silver or a magic weapon so you can damage ghosts in the event that you do encounter one.
Only Silver or Magic weapons can damage ghosts.
When you come to the closed gate in the first area of Sancre Tor, activate the Pull Lever at the bottom of the stairs to raise it. Enter the large room beyond the gate, locate the steps at the end of the corridor, and take them up to higher ground. The undead Blades encountered in Sancre Tor are likely to carry some pretty sweet magical items, so be sure to loot their remains after defeating one.
Once the undead Blade has been defeated, speak to the Ghost of Rielus that appears over the remains. He'll thank you for freeing him, and request his brothers be freed as well. With his brothers freed, together they can dispel the Underking's evil enchantment on the Shrine of Tiber Septim.
After conversing with Rielus, cross the bridge on this level and start down the passage on the other side. Follow the path and head through the door to the 'Sancre Tor, Entry Hall' area at the end of the way. Each area that branches off from the Entry Hall leads to one of Rielus' undead comrades. For the sake of following this walkthrough, head through the door marked 'Sancre Tor Prison' first.
You are likely to encounter several ghosts in this area depending on your character's level, so remain vigilant while passing through. Look to the left of the gate that you reach to spot a Pull Lever; Activate the Pull Lever to raise the gate. To open the locked door, you'll have to kill Warden Kastav to get his key. Kill Warden Kastav, remove the key from his remains, and use it to unlock the door.
Head through the door and keep heading straight; don't turn when you first have the chance. When you have a chance to turn a second time, take this turn right and head straight down the path here. At the end of the path, start downs the passage to your right. Make your way to the end of the passage and head up into the large, open area. Defeat the undead Blade here to free Valdemar's soul. With that done, backtrack to the Entry Hall.
Defeat the undead Blades to free the benevolent souls trapped inside.
Next, locate the door to the 'Sancre Tor, Hall of Judgement' area and head through. This is a small area; just head right and continue heading in this direction until you reach a large room. Take the stairs that you come to down to the blood-stained floor. Defeat the undead Blade here to free the spirit of Casnar.
With that done, make your way to the entrance to the 'Sancre Tor, Catacombs' area. If you head back up the steps that you came down to reach this floor and proceed through the south passage, you should come to the door leading to this area. If necessary, refer to the local area map and for the beginning of the path. Enter the catacombs to encounter the final undead Blade; defeat him to free the soul of Alain.
Backtrack to the Entry Hall and locate the giant door leading to the 'Sancre Tor, Tomb of the Reman Emperors' area. Head through this door to encounter the four spirits you freed. Now united, they will dispel the evil enchantment over Tiber Septim's shrine. When the way is clear, move onwards to until you reach the pedestal that holds the Armor of Tiber Septim.
The Armor of Tiber Septim is in the Tomb of the Reman Emperors, beyond the enchantment cast by the Underking many years before.
With the relic in your possession, return to the Cloud Ruler Temple and present it to Martin to complete the quest.