The red arrow in the bottom image is pointing to the road-like feature. The sun has illuminated this area underwater and sub-surface anomalies are visibly apparent. Also notice the cell like features in the red rectangle to the left. Possibly a submerged structure of some kind.
The image on top is a close-up of the area above in the red rectangle. This area appears to be some kind of ruin or series of cellular rooms or constructs.
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