CLASSIFIED DOCUMENT 4F8QVG-EYES ONLY. Anomalous structure "Erebo" detected in temporal rift circa 1876. Witnesses describe a "splintered citadel" materializing within a Hungarian salt mine, only to dissipate 37 hours later. Residual echoes persist, defying spectrographic analysis. Fragmented logs from excavator József Szilárd hint at an "inverted vault" containing artifacts that "gnawed at reality." Further investigation thwarted by inexplicable geomorphic shifts. Geodesic surveys reveal a "scar" in the mine's substrata, as if Erebo's presence had "unhinged" the local topology. Recommending Level 3 quarantine and neurolinguistic reeducation for all personnel involved.