Look for the sites I indicated on your map. The stone coffer—an Argonian reliquary—must be buried in that immediate vicinity. Locate the coffer and carefully break the seal. Make sure at least one of your number remains a good distance away when you open the coffer. I've seen such things that were trapped or had other protections and I need at least one of you alive to retrieve the meditation cylinder that should be waiting inside.
MD
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