Enter Darkfall Cave. Go through the tunnels, and past a waterfall. Watch out for the Frostbite Spiders who dwell in these caverns. Slash your way through some spider webs, then cross west on a wooden bridge. This seems to lead to a dead end, so go back on the same bridge. The bridge collapses and you fall down to the river below (if not, then just jump down) Go south on the water, dive if necessary to clear any obstacles, then go east and fall into another pool of water. If you are having trouble diving, revert out of Vampire Lord form. More Frostbite Spiders attack you as you emerge out of the water.

The cave turns north up into a small room where you find a chest with some loot in it. Then turn east and go downhill, watching out for the rockslides. Head north, east, then north, and arrive at a huge chamber with some trolls in it. Go to the west side of the chamber and find an NPC, Knight-Paladin Gelebor.

Speak to Gelebor. He welcomes you to the Great Chantry of Auri-El. This cave is a temple to Auriel (Also known as Alkosh, and Akatosh), the sovereign of Snow Elves (Falmers). Gelebor knows you are here for Auriel's Bow. He can help you get it, but first he must have your assistance. He needs you to kill Arch-Curate Vyrthur, Gelebor's brother. Gelebor believ Vyrthur was corrupted by the Betrayed, who stormed the Inner Sanctum and slaughtered everyone. Auriel cannot leave the Wayshrines unguarded. He shows you the Wayshrine.

Wayshrines were used for meditation and for transport when the Chantry was a place of enlightenment. Prelates of these shrines were charged with teaching the mantras of Auri-El to their initiates. Once the initiate completed his mantras, he'd dip a ceremonial ewer in the basin at the Wayshrine's center and proceed to the next way shrine. Once the initiate's enlightenment was complete, he'd bring the ewer to the Chantry's Inner Sanctum. Pouring the contents of the ewer into the sacred basin of the Sanctum would allow him to enter for an audience with the Arch-Curate himself.

The only way to get to Vyrthur is by following inthe Initiates' footsteps and traveling from wayshrine to wayshrine just as they did. The first lay at the end of Darkfall Passage, a cavern that represents the absence of enlightenment. There are five wayshrines in total, spread across the Chantry. Gelebor tells you that you will need the initiate's ewer. Once you've located a wayshrine, there will be a spectral Prelate tending to it. They will allow you to draw the waters from the shrine's basin as if you've been enlightened.

You can ask him some questions to learn more about his people. They were once a wealthy and prosperous society that occupied a portion of Skyrim. But they lost a war to the Nords, and asked for shelter from underground dwelling dwarves, but the price was that their entire had to be blinded.

Your next objective is to survive Darkfall Passage. Enter the structure near Gelebor and take the portal to Darkfall Passage.