Where do I find them

I activated 5 and got this achievement. You must find a nearby ruin scout and follow it until you reach the damaged ruin guard. The ruin scout will then initiate in combat, once you've defeated it you can activate the damaged ruin guard with the energy blocks.

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I got the Achievement: In the Name of Anfortas (Visit the place where the heroes met their end) after reading all recordings (all on the same day worked for me). There's another north of the 4th, southeast of the teleport point in the watery valley with the colossal ruin guard.

This is what it looks like up close.

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There is one that I found that you guys seem to have missed! Hope this helps ^^

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