Deep Team 5 identified the first tidal room during a survey of sub-level 16 in the western Underworld. Room 16-W-3, a sealed chamber approximately 5 meters square with no plumbing connections, no drainage, and no access to any water system, was found to contain 30 centimeters of standing water. The water was clear, cold, and fresh — no contaminants, no minerals consistent with groundwater, no microbial content. Pure water, in a sealed room, with no source.

We drained the room. Six hours later, it was full again. We drained it again and sealed the only entrance with waterproof membrane. The room flooded through the membrane — not through gaps or defects, but through the material itself. The membrane was intact, dry on the corridor side, and the room behind it was filling with water. We installed continuous monitoring. The room floods to 30 centimeters over a period of approximately 6.2 hours, remains at that level for 6.2 hours, drains to empty over 6.2 hours, and remains empty for 6.2 hours. A 24.8-hour cycle. Not 24 hours. Not 12. 24.8.

There is no body of water on Earth with a tidal period of 24.8 hours. The ocean tides cycle at approximately 12.42 hours, driven by lunar gravity. A 24.8-hour cycle would correspond to a gravitational influence with roughly half the orbital frequency of the Moon. No such influence exists in our solar system.

We have since identified eleven tidal rooms in the deep Underworld, all in sealed chambers with no water access. All cycle at 24.8 hours. All are synchronized — they flood and drain in unison. The water appears from and disappears into solid rock. We have placed sensors in the walls and floor. The rock is dry. The water does not pass through it. It is not there, and then it is. It fills the room as if rising from the floor, but the floor is dry until the water is already above it. It drains as if sinking into the floor, but the floor is dry the moment the water level passes below any given point. The water comes from nowhere. It goes to nowhere. It follows a tide that belongs to no moon we know.