The following is a compilation of sighting reports, incident logs, and worker testimony from the Underworld — the subterranean infrastructure levels beneath GLMZ, comprising abandoned transit tunnels, flooded utility corridors, decommissioned sublevel foundations, and unmapped spaces of uncertain origin. Reports span the period 2215–2224 and are presented in the order received. The Infrastructure Division notes that the Underworld is poorly surveyed, inconsistently monitored, and contains areas that have not been accessed by authorized personnel in decades. The reliability of individual reports varies. The consistency of reports across independent sources is noted.

Blind fish. These are the most frequently reported organisms. Tunnel maintenance crews working in the partially flooded Level -3 corridors beneath the Circuit District have reported small, pale, eyeless fish in standing water pools since at least 2215. Specimens collected in 2219 were identified as a cave-adapted morph of the common killifish (Fundulus heteroclitus), displaying complete eye regression and depigmentation consistent with prolonged subterranean habitation — likely many generations. The fish are unremarkable except for their existence, which implies a self-sustaining aquatic ecosystem in the flooded Underworld levels that no one has surveyed.

Albino rats. Workers and Underworld residents consistently report rat populations in the deeper levels that are significantly larger than surface populations, fully depigmented, and — according to multiple independent accounts — coordinated in ways that exceed the already-anomalous behavior documented in surface rat populations. An urban explorer operating under the handle "Depthwalker" posted a widely viewed recording in 2222 showing a group of approximately thirty albino rats moving in formation through a Level -5 corridor, stopping at intersections, and apparently responding to vocalizations from unseen animals deeper in the tunnel system. The recording has not been independently verified but is consistent with other accounts.

Luminescent fungus. Multiple reports describe fungal growths in the deeper levels that emit light when disturbed — a faint blue-white glow that intensifies with physical contact or vibration. Specimens have not been successfully collected, as the fungus degrades rapidly when removed from its substrate. The luminescence appears to be a stress response, possibly serving as a warning signal. To what, and from what, is unknown.

The tracks. Beginning in 2220, work crews in Level -7 and below have reported finding tracks in the silt and sediment of deep flooded corridors. The tracks are described consistently: four-toed, approximately 20 centimeters in length, with deep impressions suggesting an animal massing 80–100 kilograms. They do not match the track morphology of any animal known to inhabit the Great Lakes region — or, when submitted to the GLMZ zoological database for matching, any animal in the database at all. The tracks are always found in flooded corridors, always heading deeper into the tunnel system, and never accompanied by return tracks heading back toward the surface.

The breathing. This is the report the Infrastructure Division is least comfortable including, but it appears with sufficient frequency and consistency to warrant documentation. Workers in the deepest accessible levels of the Underworld — Level -8 and below — report hearing, in the silence between their own movements, the sound of breathing. Not mechanical ventilation. Not water flow. Breathing. Rhythmic inhalation and exhalation, slow and deep, emanating from deeper in the tunnel system. The sound suggests a large animal — significantly larger than anything that should be able to enter or survive in the tunnel infrastructure. No visual confirmation has been obtained. No source has been identified. The sound is always described the same way: too large. Whatever is breathing in the deep Underworld is too large to be in a tunnel. And yet the sound is there.