This is for access to the Haunted Vaults, aka Lower Stormguard Halls, and is required to advance the Signature quest The Stormhammer in Kaladim. You can complete it without doing the Stormhammer, but you will need to do it again if you take the series. Completing it prior to doing the Stormhammer series will not give you access to the Haunted Vaults.
There is now a trapdoor hatch where the rug was. If you are on the Stormhammer Signature series and can speak the Serilian (Kobold) language, then completing this quest allows you to see the note when examining the vault door.
To get the key to open the vault, go to the waterfall and kill the kobold ring event mobs on the cliffs in front of the waterfall by the bridge. (Ring Event Notes) It drops off one of the spectral mobs in the third wave of the ring event: a deathwatch exorcist or Reverend Rutzkill.
Note: the above may be the old way of getting the key, or simply the harder way. You can kill A Terrok warlord at ( 161, 17, -65 ) /waypoint 160.5, 17, -64.5 for the key.
Once you get the key, return to the room where the bear rug is and right click the vault door to enter the Haunted Vaults.
Note: If the bear rug respawned, you can target the vault underneath the rug.
WARNING: To zone into the Haunted Vaults, group members must not be further along on the quest. You will not see the option to enter the vault if any one member has already gotten the 3 subquests. Use invis when zoning in as there are 2 mobs in the room as you enter.