Dimmed Bones is a ruin site in Horizon Zero Dawn. It appears to have been a communications facility, recognizable from the collapsed satellite dishes. Aloy encounters the site while helping Erend solve the mystery surrounding his sister Ersa.
During the time of the Old Ones, the site was likely used for communications.
Dervahl called Ersa to the site with an offer to parlay. When Ersa and her Vanguard arrived, they were overwhelmed by Dervahl's sonic device and defeated. Ersa was stripped of her armor and captured, while the rest of the Vanguard were killed by Dervahl's forces. The bodies of the Vanguard were placed in Red Ridge Pass, surrounded by Shadow Carja armor, giving the illusion that they were ambushed by the Shadow Carja instead. To prevent the Carja from searching for Ersa, another body, whose face was mutilated beyond recognition, was placed in Ersa's armor.
A Foil Exposed
Hungry for revenge against the Shadow Carja, Ersa's brother Erend enlisted the help of Aloy to find the soldiers responsible. After noticing peculiarities with the supposed murder site, Aloy found cart tracks leading to Dimmed Bones. Erend and Aloy followed them to the real ambush site, where they were ambushed by Dervahl's followers. Once their enemies were vanquished, Aloy deduced what truly happened, and that Ersa was likely still alive.
Metal Flower II (I) is nearby