To get the "Key" I had to steal it again from Tatar the Lake keeper, which you get "Eliza's Small Treasure Chest" from.

Also you need 5 Beer (those for workers, you can buy it from marketplace or cook the recipe yourself) on your inventory and 10 Energy Points to complete this quest.

Fresh beer(blue quality) WONT WORK! You need SIMPLE(green) Beer..
Свежее пиво не покатит, обычное зелёное пиво для работников..

Turn off Auto Arrange Inventory to open the box.

Buy 5 beer from market place.
Have Energy to steal key from Tar Tar and learn knowledge from him

Yeap, I confirm ALL of the above; you need to steal the key AND to give him beer . . . Not the one bought from the cooker, not any other - just the plain simple 'green' worker beer... Need 20 energy (10 + 10 ) for the 'story', can't be sure about the stealing - it took me 3 times to get the key but you maybe lucky and get it right away!

You can steal beer from Tartar, and it is a fairly common stolen item. Took 3 mins to get 5 from him- so if you feel cheap or there is none on the MB release your inner thief!

Acheter 5 verres de biere.une fois les verres de bière donner a tatar ecouter son histoire.Attendre environ 3 min et lui voler la clé (f6) se mettre pile poil au niveau du pnj pour voire le menu afin d’éviter de se faire prendre la main dans le sac aligner la cle et le coffre verticalement afin de l'ouvrir.

Pazardan 5 tane bira alın, Tatar'a gidin, hırsızlık yapın, anahtarla sandığı birleştirin, r r yaparak geçin Tatar'ı. Afaru'ya birleştirdiğinizi verin.

Petite question si on a perdu la clé lors des premières quetes quand on trouve le coffre on peut le ravoir ?

1) Go to the market and buy 5 green beers (of those that you give to recover energy of the workers)
2) Now go to Tatar and ask him about Eliza. He will say he wants five beers to tell you the story. Give him the beers and talk to him twice to finish the story (you'll spend 10 energy)
3) Go behind Tatar and press F6 to steal from him until you get the key (you'll spend 10 energy each try). I got the key on the third attempt (30 energy spent).
4) Unmark inventory auto arrange and place the treasure box you got in the last quuest on the left side of the key you just stolen from Tatar and press the + button to merge the items. That will open the treasure box.
5) Go to Afuaru (quest giver) and finish the quest.