YOu can open the thrice locked Chest by completing the DF Quest chain, just accept it from one of the npcs near the spawn point. It makes you collect 9 different keys from the bosses of DF. The keys come in 3 sets, each of which can be combined into a golden key. The 3 golden keys can then be made into a golden keychain or something, which will open the chest.
For some reason, you can't always accept the quest (worked fine on my first character, didn't work on one I consoled up to lv100).