Round the corner the corridor widened out into a spacious hall. To one side a flight of stone stairs ran upwards; opposite these, another flight ran down into blackness. On each side were two doors, and a fifth door faced her--an incongruously elegant portal of polished oak adorned with grotesque carvings and half masked by rich velvet hangings. The soles of her supple shoes made no more than a soft slithering sound on the concrete floor as she moved forward. At the end she paused undecidedly. That fifth door was intriguing; intriguing also, after the janitor's vague references to a tunnel, was the flight of stairs that disappeared in the direction of the vaults. Susan solved the problem in a reckless way that would have earned the admiration of Smiler: she took a coin from her pocket and held it between her palms. "Heads the stairs, tails the door," she murmured, and opened her eyes.... Heads. A whiff of dank, clammy air met her as she felt her way over the first step. Luckily, the stairs were concrete, as was the upward flight, and there was no danger of creaking boards or a rotten tread. Her light showed her a small landing where the direction reversed. She took the corner and continued downwards. The cellars seemed to extend over the whole ground space of the building, most of the weight of which appeared to be taken by a number of massive pillars. She could only guess at the actual area, for little but the ceiling was visible. Every available cubic inch of space was filled from the floor with great mounds of earth, tightly packed. There must have been tons of it, piled and compressed into stacks. All the thoroughfare that remained was a narrow lane which wound between the huge dumps, and these had been buttressed up on either side of the path so that the last fraction of volume might be utilised. Down this lane danger lay, for in that insignificant width there was not much chance of avoiding anyone who happened to be coming towards her. Moreover, the path was lighted at intervals by electric bulbs fixed to the side boarding. Switching off her torch, she transferred her automatic from her hip to her jacket pocket, where it would be quicker to reach, and went on. There was a silence in that weird cavern, which was accentuated rather than relieved by the dull rumble of the plant overhead. That the true purpose of this plant was to provide power she gathered from the insulated cables which snaked along on each side.