By dusk they were back at a neglected shelter set off from the bright paths, a place half claimed by climbing plants and mostly ignored by the passing crowd. The canal beyond had turned dark blue, almost black under the first lights. Elias found a flat stone table and cleared it with his forearm. The movement pulled at his side hard enough to make him stop and breathe carefully through his nose before continuing.

He used bits of charcoal from an old light basin and a pale chip of broken tile for contrast. On the tabletop he drew the ring symbol first. Then the surface gardens. Then the lower shafts. Lines between them. Arrows for cargo, air, waste, people. He marked the tower at the meeting point, then circled the hall, the mural spine, the hidden vents, the active interfaces. As he worked, Lina sat opposite with her chin on her knees, watching each mark appear as if it might become a creature and stand up.

"This part," he said, tapping the orbital ring, "holds archives, governance, maybe more. Remote enough to survive weather and unrest. This part"—he drew the surface wider—"is the managed public world. Beauty, rest, guided behavior, almost no need to retain practical knowledge. And this below—"

He stopped. The undercity was still mostly blank because he did not know enough to draw it honestly.

"The hidden people," Lina said.

Elias tapped the sketched routes with the charcoal. "Yes. Maintenance, transfer, repair, maybe farming, maybe intake, maybe enforcement. The whole thing linked through the tower and these service routes."

She leaned in, eyes following the arrows. "And the old bad water? The hot years? The storms?"