The chest is in the fjords. You can return to Broken Valley (might want to level a bit first), though it doesn't quite look like it used to.

BTW, I waited until I was done pretty much everything before heading to the Hall of Echoes (level 37) to open the Germory chest thinking that would help get better equipment (results in the spoiler below), but trying again with a level 25 save the contents in a couple reloads were pretty comparable.

In the Gremory treasure chest I got 3 divine charms and a couple pieces of equipment I couldn't use. On the second try I got an epic bracelet (+3 Poison Arrow, +8 Dexterity, +9 Ranged Damage) with 3 charm slots and 3 enchantment slots. I use splitting arrows (which is on my current bracelet) more than poison arrows, so except for the extra enchantment slot this wouldn't be a great upgrade. The forth try gave epic earrings (+3 Ranger Strength, +7 Dexterity, +7 Ranged Damage), also with 3 charm slots and 3 enchantment slots. Another 4 or 5 tries (while I was doing something else) gave two epic pieces of jewellery: earrings (+3 Splitting Arrows, +8 Dexterity, +5 Heightened Reflexes, 3 charm slots, 2 enchantment slots), a good upgrade for my current legendary earrings (+2 Poison Arrows, +8 Dexterity) and a bracelet (+3 Explosive Arrows, +8 Dexterity, +7 Ranged Damage, 3 charm slots, 3 Enchantment slots), an upgrade for my current one (+3 Splitting Arrows, +10 Dex, +6 HR).