You have been sent here to investigate what exactly the roekillik are digging for. Surely they wouldn't toil in the frozen halls of Permafrost out of their own free-will unless being persuaded or forced to. Something is definitely afoot and only a team of brave adventurers can solve this mystery.
As you cross the bridge leading to the citadel courtyard you will notice you're getting stunned and silenced frequently. This is because of the two Frostpaw sentinels guarding the ramparts above the front gate. To deactivate them you must interact with a crystal on a wall deep within the citadel at ( 74, -28, -384 ) /waypoint 74, -28, -384.
If you failed to kill Kodan on your first attempt, when you resurrect, Kodan's fight mechanics will still be active. There are two idols in the cave where he spawns from that shoot a beam at a player for massive damage every few seconds as well as stunning/rooting. They have no line-of-sight. To disable them you must use Rygias Amulet of Dousing, received during the quest Harness, while standing near them. Unfortunately the only resurrection point in the instance is at the zone-in, far from these idols, and as such it can be frustrating to make the return journey. You can brave the slow walk back, or wait out the minimum lockout period of ninety minutes, reset and attempt again.