Enter Darkfall Passage through the portal near Gelebor.

Touching the Sky
I've encountered Gelebor, a snow elf Knight-Paladin of the Chantry of Auri-El. He's requesting I kill his brother, Arch-Curate Vyrthur, who's been corrupted by the Falmer. I've been given an Initiate's Ewer which will ultimately provide me access to the Chantry's Inner Sanctum where both Arch-Curate Vyrthur and Auriel's Bow are located.

Survive Darkfall Passage.

Close to the entrance of the passage, a Chaurus Hunter Fledgling attacks you. Defeat it, and continue through the narrow passage behind it. When you come to a small body of water, a Falmer Skulker jumps from above. After killing it, continue east and defeat the Falmer Gloomlurkers and Nightprowlers on the way.

Soon you get to a big chamber with flowers and waterfalls. Kill the Falmer Warmongers and other enemies in this area. Go to the west side of the chamber and climb up a platform to the north. Then, turn west. There is a chest here near some Gleamblossoms, but watch for the trap above.  Go west past some glowing bluish rocks, then turn south into a misty corridor, then east. Watch out for Tripwires on the ground that set off traps.

Go north and east through another long dwindling corridor. It turns west eventually, and your each what appears to be a dead end, but note the Rope Releases on the wall. Activate them to reveal another section of the passage. A Vale Sabre Cat is waiting for you on the other side, kill it.

Reach another huge room full with aquatic plant like beings. Climb up the ramp in the center.

Your task now is to Fill the Initiate's Ewer. Talk to Prelate Sidanyis near the Wayshrine of Illumination. Watch him open the Wayshrine. Then, Draw water from the basin. This fills up one of the five Ewers required. Use the portal to advance to the next section, Forgotten Vale.