Frostmourne Cavern
From WoWWiki
Frostmourne Cavern [74.3, 23.7] was the cave that held the runeblade Frostmourne prior to being claimed by Arthas Menethil.
In the Alliance quest Frostmourne Cavern, players can see a flashback of the last interactions between Arthas and Muradin Bronzebeard (as originally seen in Warcraft III), with a surprise ending indicating Muradin's survival. Next to Frostmourne's altar lies Arthas' forgotten hammer, frozen in the snow. The cave is also teeming with saronite, indicating a connection between the Lich King's power and Yogg-Saron.
