To step off the edge of an inverted mountain inside the hollow core of the Earth was to surrender every living instinct sharpened by four billion years of surface evolution.
At the outer apron of Vault Six, the iron-hard metal roadway simply ended. Beyond the final polished flat stone slab lay no safety railings, no dropping stairs, and no lower terraces. There was only a yawning, three-space-folding deep pit of open sky space spanning over six thousand miles in every direction.
Looking “down” meant looking into the sky. Looking “up” meant looking at the concave continents of stone-glass forests and glowing crystal oceans that wrapped around the squad in a huge, ball-shaped shell.
Arthur Vance stood at the cliff edge, the wind of heat updrafts tugging at the charcoal hem of his carbon-weave trench coat. His boots were magnetized to the rim of the iron-hard metal plate. But his inner ear, disoriented by the curved horizon, demanded that he step back.
“Titus,” Arthur said quietly over the squad hum. “Carriage protocol. We take the low gravimetric lane.”
Behind him, the ancient terrapin didn’t hesitate. Titus lumbered past Arthur, his four massive, columnar legs moving with rhythmic, unstinting patience. As the terrapin’s front claws cleared the edge of the deep pit, his heavy fourteen-ton body didn’t plummet like an iron anvil.
