Touching the Sky (quest)

Walkthrough
After reading the Elder Scrolls with the help of the Ancestor Moths...

Locate Auriel's Bow
...it is now clear where Auriel's Bow can be found, in the Darkfall Cave.

Explore and clear the cave maze until you find a structure set into the ground, a Wayshrine as it turns out, next to a Shrine of Auriel.

Speak to Gelebor
Here Knight-Paladin Gelebor, one of only two known Snow Elves (the other one is his brother Arch-Curate Vyrthur), is standing guard at the Great Chantry of Auri-El and the portal to the Darkfall Passage. Gelebor is quite aware of why the Dragonborn has shown up, it is for Auriel's Bow of course. He is even willing to help retrieve it, if the Dragonborn looks into the matter of taking out his insane brother Arch-Curate Vyrthur.

The only way to get to his brother and the bow is to take on the role of an Initiate, and pass the Wayshrines one by one. For this an Initiate's Ewer will need to be dipped into the Wayshrine basins. Only after finding all five Wayshrines will the path to the Inner Sanctum, where Vyrthur has holed up, become accessible.

Survive Darkfall Passage
Gelebor opens the Wayshrine here in the Darkfall Cave, inside there is such a basin (empty) and a portal leading to the Darkfall Passage. The Wayshrines are not only a place of mediation but also a very sophisticated transport system.

Enter the portal and make your way through the Darkfall Passage.

Fill the Initiate's Ewer
Navigating a long-winding maze of caves and even enormous Forgotten Vale with the Glacial Crevice and finally the Sharpslope Cave the Dragonborn will be directed to the locations of all the Wayshrines, filling up the Initiate's Ewer on the way.

Obviously, this does not go without a significant amount of resistance from Falmer and other critters.

Gain entry to the Inner Sanctum
Finally, at the gates to the Inner Sanctum the ewer admits the Dragonborn.

Locate Arch-Curate Vyrthur
Exploring the icy passages in the large complex leads to Arch-Curate Vyrthur in the Chapel.

Confront Arch-Curate Vyrthur
Vyrthur obviously has no intention of unhanding Auriel's Bow, and will let reanimated minions soften up the Dragonborn. But that fails.

Slay Arch-Curate Vyrthur
As Auriel's Chapel collapses, with a spectacular view of the Forgotten Vale from the balcony, a showdown with Vyrthur cannot be avoided.

Speak to Gelebor
After Vyrthur's death, Gelebor will appear, offering, as promised, Auriel's Bow as a reward for killing his insane brother.

Retrieve Auriel's Bow
Simply walk over to Auriel's Bow and pick it up. Gelebor can turn normal Elven Arrows into Sunhallowed Elven Arrows that will be of use later in the quest line. Serana can now be asked to spill her blood on some Elven Arrows, this creates Bloodcursed Elven Arrows.