1. Go to Strath with any character.
2. Teleport to the Large Solid Chest spawn zones.
3. It spawn in 4 locations (random) in conjunction with a Large Bound Mithril.
4. Teleport under it, set your self and Z up to avoid agro. Loot it - repeat.
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I rather not tell the location to avoid them getting nerfed. If you know where they are keep it to yourself please.