Justinan sends you to Everfrost to work with Kaira L'or again to open the Vestibule of Righteousness.
Kaira can be found at ( -167, 46, -680 ) /waypoint -167.09, 45.62, -679.63. From the zone in, swim to the western shore, head up Bitterwind Trench, go right at Jagged Plains, and through Icespire Caverns. Kaira is at the end of it.
Kaira is injured and dies when you speak to her. Before she dies, she warns you how strong "The Guardian" is.
Enter the Vestibule by clicking the boulder right next to where Kaira was.
Mobs inside are Vestibule defenders, frosty pests and frosted bubbles, ranging from level 60 to 63. Defenders will be non-aggro if you've never gained their hate by killing any of the winged maidens outside.
There are three clear globes which are the Sacred Vessels in the cave: one to the right, left, and behind The Guardian. To get the Vessels, head forward across the bridge to The Guardian and speak to her at ( 7, 4, -641 ) /waypoint 7, 4, -641. She gives you a puzzle to solve. If you choose the wrong one, you fight her and still gain access to the Vessels, but you lose some deity favor. The correct answer is 11.
NOTE: There are wandering aggro solo monsters. Goblins (a frosty pest lvl 60) and blobs (a frosted bubble lvl 60). They path around the plateau.
Once you get access to the Vessels, click the Vessel where The Guardian was. Choose "Touch the key to the vessel" and "Study the rune key." in the dialogue that appears. Then click the Vessel to the north at ( 65, -1, -643 ) /waypoint 65, -1, -643, and finally the last one to the south at ( 24, -1, -564 ) /waypoint 24, -1, -564. The keys become the Gavel of Entry.