Blood Key

Source

 * Thrall can find this in The Oracle, chapter 7 of the Warcraft III orc campaign, The Invasion of Kalimdor.


 * Arthas Menethil finds this key in Into the Shadow Web Caverns, chapter 7 of the Warcraft III undead campaign, Legacy of the Damned.

In the RPG
In Doorward there is a massive, blood red door leading down to the depths of the Old Kingdom. The door is locked, and Baelgun Flamebeard holds the Blood Key that opens it.