Its in a quest
You use some incense to enter the spirit world then you're supposed to avoid the valks and LK and find the secret vrykul
And when in the spirit world there's Lich King with about 30M health, if you go near him he flattens you to the ground with a 2minute debuff and after about 1:30 he kills you after talking a bit.
you can click the incense buff off and live and just wait out the debuff.
I had forgotten what I was suppose to find so I let LK kill me thinking that might be what I was supposed to find, BTW its not.
You're suppose to find this one house that has a mother and father Vrykul that had a human baby and they're worried about their king finding out, so they send the kid far away (some on wowhead think the kid could be the human orphan in shattrath, but timelines wouldn't fit)
What you've never done that quest chain?