Thoralius the Wise wants you to search Nifflevar while you are in the spirit world and find information about the Secrets of Nifflevar.
All that we know of the vrykul indicates that they only recently appeared in Northrend. Why, then, are we seeing vrykul in visions that date back 15,000 years? Surely if the vrykul had previously existed in Northrend we would have known.
You must press on to Nifflevar. To get there you must go northeast, through Wyrmskull Village, and take the path leading up through the dam. Nifflevar is on the bluffs of the fjord.
Use the incense burner once you arrive at Nifflevar and search the area for clues.