Sky

They encountered otherness and found it too other to be valuable.

Ecumenopoleis

Self-sufficiency is general far simpler than importing food, but this is also done.

Ones

The nameless are defeated by their own existence.

Tunnel

Reality itself may be opposed to giving away the answer; the depths of existence falls infinitely forward.

Logic

The trail from one to end to another is clear, but only if the path is immutable.