The last honest map ends where the known rock ends, and below that the rope begins. Every expedition pays out its own knotted return line, hand over hand, a knot at every turning. A tuned bell rings at the head of the file and another answers from the rear. Three witnesses walk where one would do, and up in the hold someone who will never come down keeps the memory of the way for them. Then the stone forgets its order. Bands of old star-metal glint in the lamplight where no seam should run, laid above rock that ought to lie beneath it. A door stands in the wall, square and patient, and no hold has ever claimed its making. You call out, and the echo comes back with a word missing. On a carved slab the lines run clean until a name should be, and there the stone is smooth. Further down, the bell behind you stops answering.
What lies below
The Underdeep is what the Stonebound call the depths below ordinary mines, where direction, memory, echo and the order of the rock all become unreliable. It may be one connected place, many separate wonders, or simply the word for the point at which maps stop deserving trust. A mine does not become Underdeep at any fixed depth. It becomes Underdeep when the known layers and the dependable way back both fail.
The surest entrances lie beneath the Blackspine, though old records hint at passages running far beyond the mountains. No surface map can show how far it reaches. Expeditions still go down, because ore, lost testimony and perhaps answers lie below, and because leaving the depths unwatched may be worse.
What is told
Fragments suggest that someone explored down here before the oldest Stonebound holds were founded, but no unbroken chronicle survives. The carved records found below are tied to Nhal, the Hollow Star: they lose names, or disagree with copies made elsewhere, and no one knows whether Nhal is a being, a force, an absence, or several things under one name. The disaster of the Broken Bell happened in a deep chamber, and after it many holds closed their tunnels to outsiders, fearing too that war would turn unknown structures into weapons. Since the Warm Shaft was opened, the mountains have pulsed with the heat of Vuldra, the Heart Under Stone, and beneath some forges a second, slower rhythm is heard that no one can explain.