After 'slipping' and pressing the wrong trigger on my hotas, I came away with the prism / ancient artifact from one of the etowers in the ruins. This allowed me to view it from all sides, incuding the lower end, and this showed my initial thought of two interior shapes existing was correct. There's a d20 shape surrounding a sphere inside the prism about a third of the way from the top, where the light is emitted from seemingly. I didn't need to clip with the debug camera to see this too, which was nice.
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The sunlight was in the right place for a good shot of the linear features of the ruins, which I'll post once it's finished uploading. I'll appologise in advance for all the tire tracks from my SRV that can be seen (impressive detail from 1.5km up)
I had to convert the bitmap to a jpeg before uploading would work... oh well.
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Enjoy!