Online:Climbing the Spire

Quick Walkthrough
#Talk to Holgunn.
#Lower the first set of wards.
#Find Walks-in-Ash.
#Lower the second set of wards.
#Talk to Tanval Indoril.
#Get the key from Flamespinner and lower the final ward.
#Talk to Tanval.

Detailed Walkthrough
Speak with Holgunn. Walks-in-Ash followed close behind Tanval when he first entered the spire, and managed to get a few troops into the mountain. The wards snapped shut very soon after she entered. You need to lower the wards so Holgunn and his men can get in. Once you've lowered the left and right wards, enter the Tormented Spire. Now you need to find Walks-in-Ash and see what she knows about Tanval's plan. Head northeast, weaving around and avoiding as many Vanguard troops as you can. When you reach her, she's kneeling behind a Daedric archway, concealing herself from the Vanguard. 
Talk to her. Apparently, there are two more wards that she knows of that are in the way of your climb, both on the way up the spire and located within Daedric ruins. The Southern ruins are closest. Sneak past the Vanguard and enter the Southern ruins. Near the ward is an ancient guardian of the Tormented Spire: Hatewarden. Defeat Hatewarden and lower the southern ruins ward. The Northern Ruins are on the other side of the mountain. Keep running north, past the glowing blue screaming death ritual performed by several vanguards and the warded off passageway. Enter the ruins, defeat the guardian Brimstone, and lower the northern ruins ward. When you've lowered both wards, find the Pact commanders. Exit the Northern ruins and take a right at the giant, burned up tree just outside the ruins. The red mist that once blocked the way is now gone since the wards have been deactivated.Head through that Daedric passageway and you'll find someone very special on the cliff overlooking the volcano's caldera: Tanval Indoril himself, surrounded by your commanders. Speak with Tanval and ask him why he's hurt. 
Tanval says that he was injured by Daedra summoned by Sadal the moment he entered the premises. He's lucky to be alive. Tanval can't control Sadal, even with the Coral Heart in his possession. He regrets his outburst, and wants to help you rebind Sadal. However, there's one final ward blocking the way to Sadal's prison. You need to enter the Caldera Ruins and take down the Shadow Ward within. The key to the ruins is held by an ancient guardian named Flamespinner, a giant Spider Daedra. You need to use the summoning bowl in the center of the caldera to bring her to the Tormented Spire, and defeat her for her key. The key given to you by the grandmaster of House Dres won't work on the ruins. Head down the path to the center of the caldera, defeat Flamespinner, and use her key to open the Caldera Ruins on the far west side of the caldera. You can't miss it, you pass by it on your way to the center. It's a large Daedric door, just like the Northern and Southern ruins. 
Within the Caldera ruins lies the Shadow Ward. Within the ward's holding chamber are many moving fountains of shadow, which will send you to the top of the stairs when you touch them. Avoid the shadow fountains and lower the final ward, then talk to Tanval Indoril outside the Caldera ruins for a fair sum of gold and your next quest.
  

Quest Stages