This chest is located on 60.90, 37.85,in Zereth Mortis, behind the pyramid.
This chest can be obtained once per day.
There is another chest located at 61.42, 17.64
There is a third one located at 64.82, 33.69 (see map)
How to open Sandworn chests
Kill special mobs called Mawsworn strikers. You will find many in this area.
These mobs have a chance to drop an item called Sandworn Chest Key Fragment.
There are also other mobs suck as elite Nathrezim Acanist in the same area that also can drop it. 
Once you have gathered 5 fragments, combine them and you have the key to use on the Sandworn chest.
This chest contains:
- 22 Sandworn Relics
- 6 Cyperhs of the First Ones
- 7 Anima items (35 anima in each)
What are Sandworn Relics used for
Check out my guide here.
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