Once clear of the body, I hurried onwards on trembling legs, until the corridor straightened and entered a large space filled with a knot of corrugated pipes and tubes. Water dripped from leaky joints; steam hissed. Some of the pipes were copper-coloured and pencil-thin; others were made of tough black ceramics, and were as wide as subway tunnels. I couldn’t see the roof or the floor. A metal catwalk led me through the tangle. In places, I had to duck or even crawl.

At the far side of the tangle, I came to a door. Like the door to the flying elevator, this one seemed to be made of a thick transparent glass. Beyond lay an unlit space of indeterminate size. The bottom of the door had jammed a few centimetres from the floor. I knelt in front of it and tugged a hair from the back of my head. When I dropped it, it fell slowly until drawing level with the gap, at which point it jerked and swirled back towards me. Whatever was causing the breeze lay on the far side of this obstacle, and I hoped it was a stray air current, blowing down into these sterile tunnels from an opening on the surface.

I took hold of the base of the door and tried to heave it upward. Then I braced myself on the floor and tried to move it with my boot, but despite my best efforts, it remained resolutely in place. I realised that if I wanted to get past, I would have to lie on the floor and squeeze through the gap.

I flashed my torch under the door, but could only see an expanse of bare floor stretching away.

Reluctantly, I rolled onto my front and used my hands to propel me backwards until my feet had passed beneath the barrier. The lower edge of the door scraped my backside, and I was seized with a sudden, heart-thumping fear that it would capriciously unstick itself and fall shut, slicing me in two. I wriggled harder, dropping my shoulders and turning my head sideways until my cheek touched the smooth floor. Then I was through. I took a moment to compose myself, and then turned to survey the gloomy interior of the room I’d entered.

The walls here lacked the internal luminosity of the walls in the rest of the ziggurat. The residual light from the corridor threw my shadow in front of me. Hesitantly, I took a step forward, testing the floor with my boot before trusting it with my full weight. Then another.