These Hills Sing

First of all upvote Elongwi for discovering the spot. This was really hard!

1. 
   
2. Collect Discarded Lunchbox treasure (1 x [item=160485] inside, DON'T OPEN IT.
   [object=293349] is part of the Treasures of Stormsong Valley so you have probably already collected it
   
   
3. 
   
4. You can always buy more Luncheons from (buy multiple just to be safe... it's 4-min run after all)
   
   • 
     
   • Horde - Sanya Wraithschilde in Warfang Hold
   • 
     
   • Alliance - "Nasty" Buck in Brennadam
   • 
     
5. 
   
6. Go to the mountain and open Luncheon at 41.25 69.53 (map)
   Entrance to the top is from the west side (Area with elite Ettins)
   
   • 
     
   • Dismount before use or it can bug and you will have to run all the way back
   • 
     
   • Have 2 free slots in your bags
   • 
     
   • Make sure you are out of combat
   • 
     
   • Must be standing, don't lay/sit down
   • 
     
   
   
7. 
   
   


In Stormsong Valley:
/way 58.21 63.68 Step 1 Discarded Lunchbox Treasure
/way 41.25 69.53 Step 2 Open An Unforgettable Luncheon

/way 58.63 70.27 Alliance vendor: "Nasty" Buck
/way 50.93 33.71 Horde vendor: Sanya Wraithschilde


Here is demo of the process: https://www.youtube.com/watch?v=tI67pZ7KkYQ

PS: if you just looted the treasure, relog to be able to open it and to buy more from vendor. Bugged for me.
You can buy multiple items, will take different slots in your bag.

Tomtom coordinates are 41.45 69.50

It is at the top of the hill with a rug and pillows, etc.

To earn These Hills Sing achievement you need to do the following things:

• 
  
• First, you need to find [object=293349] treasure. It's located at 58.4 64.0 point in the shad.
• 
  
• Do not open [item=160485] that you found in the lunchbox.
• 
  
• Take [item=160485] to the top of mountain at 41.22 69.51 point, dismount and open it. Beware of elite ettins over the area.
• 
  
• Get your These Hills Sing achievement
• 
  

These Hills Sing achievement - https://www.youtube.com/watch?v=90XQkcgtap8

Okay, but what if you already looted the treasure and opened / sold / lost [item=160485]?
If you have looted [object=293349], you can now buy luncheons from vendors.
Horde vendor - Sanya Wraithschilde, Warfang Hold / Alliance vendor - "Nasty" Buck, Brennadam.
And one more thing, seems Alliance should complete quest chain at Brennadam Square to be able to see [object=293349]. May be fixed already.

TomTom:
/way Stormsong Valley 58.20 63.69 Discarded Lunchbox (on the top of keg shelf)
/way Stormsong Valley 41.22 69.51 Mountain to open An Unforgettable Luncheon

/way Stormsong Valley 50.92 33.70 Sanya Wraithschilde Vendor Horde
/way Stormsong Valley 58.62 70.26 Nasty Buck Vendor Alliance