To Rise and Decline

 is a quest in.

Synopsis
According to Vatnir, a portal into the White Void has opened deep within the Dead Floe, fueling the iceberg's growth. While Vatnir wasn't certain why the Dead Floe is spreading, he suggested that the Watcher begin their search at the Vytmádh, an entrance to the Beyond hidden in a temple at the center of the icebound island.

Walkthrough

 * After the introduction to the dracolich and the reveal that Vatnir is a lot more reasonable than initially seen, head out to climb the glacier. As you come out, the corpse of the dracolich pulls away and disappears into the clouds above the glacier, meaning you'll have to try to kill it again (and that the Watcher's usual kill-problems-until-they're-no-more approach might not be enough here). Head to the Outcrop on High (the location is at the northern end of Harbinger's Watch), then navigate to the Temple rope in the northeast.
 * After sliding down, make your way down to the Temple through the caverns. Enter it and head further to witness the dracolich being sucked through the portal into the White Void. Interact with the portal to gain an audience with Rymrgand, who will state in no uncertain terms that he doesn't care if the Deadfire freezes over. However, since the dracolich's very existence is a bruise on the ego, the god will offer you... A deal.
 * Save before trying to spit in Rymrgand's face. It's worth it, even if you are frozen from the inside out.
 * Otherwise, to access the Void through the Vydmath, you need to first agree to a favor - killing the Dracolich for Rymrgand - and then find his eye in the temple.
 * To gain the artifact, head to the eastern cave from the lowest level and interact with the ice imp. Try to take its "white ball" to make it come alive. Then you can convince it to hand it over with Intimidate 8, or ask what it is and reply with Diplomacy 11 or Religion 8 when the imp proves adamant. Alternatively, you can try to trade for it, using Bluff 15, offering 20 000 or 8 000 copper, or by giving it the stone idol found in Vatnir's secret room at the Watch and following up with Bluff or Intellect 10. The only option that works is offering it 20 000 coins or the bluff option with stone idol, as any imp is going to have a weakness for those. Otherwise, you need to fight through four rime constructs to get the Eye of Rymrgand.
 * Afterwards, return to the portal and enter Rymrgand's domain.