The empty train I had stowed away on moved for days over the bridge, sometimes slowing but never stopping. I could have jumped from it a couple of times, but I might have killed myself, and I was still determined to reach the end of the structure. I had the run of only three deserted carriages, two passenger cars - with seats and small tables and sleeping compartments - and one dining-car. But no kitchen-car, no galley, and locked doors at each end of those three carriages.

I hid most of the time, slouched down in one of the reclining seats so that I could not be seen from outside, or lying in a sleeping compartment top bunk and peeping out through half drawn curtains at the bridge outside. I drank water from the toilet washbasins, and day-dreamed or dreamt about food.

The carriages were unlit at night, haunted by the flickering beams of yellow-orange light from outside. It grew gradually warmer with each passing day, and the sunlight outside became brighter. The overall shape of the bridge outside the windows did not seem to change, but the people I glimpsed occasionally by the trackside did alter; their skins became different colours, darker as the sunlight increased.

After some days, though, everything seemed to get darker again, as I lay, faint with hunger, rattled like something loose in a long, reclined seat. I began to believe that the light had not changed at all, and that it was something inside my eyes that made the people look like shadows. Still, my eyes hurt.

Then one night I awoke, dreaming of the last meal I had had with Abberlaine Arrol, and saw that it was very dark, both inside the carriage and out.

No glow of light came from the bridge outside, no chrome edge of reflecting cabin fitments was visible; neither was my own hand when I held it in front of my face. I closed my eyes and pressed them, only then seeing the false nerve-light that is the eyes' reaction to pressure.

I felt my way to the nearest outside door, opened the window and stared out. A strange, thick, heavy smell came into the carriage on the warm air. It alarmed me at first; no smell of salt, of paint or oil or even smoke and fumes.

Then I saw a faint edge of light above me, moving very slowly. The train was still moving at close to full speed - the slipstream poured roaring through the window to tug at my loose clothes - but whatever it was I could see, the light was moving very slowly over it; it must be very far away. A cloudbank, I thought, lit by starlight, then realised I could see that outline of light continuously, without any interrupting beams and girders chopping the sight into flickering fragments.

A part of the bridge where the load-bearing structure was beneath the level of the rails? I started to feel faint again.

Then the train slowed for some points, and before it speeded up again I could hear, through the lessened noise of its progress, the distant night noises of a dark, wild forest, and saw that the edging of the light I had mistaken for a cloudbank was a raggedly wooded ridge a couple of miles away. I laughed, delirious and delighted, and sat by the window until the dawn came up and made the green forest steam with fragment mists.

That day the train slowed, and entered the outskirts of a sprawling town. It wound sinuously, slowly, through a great marshalling yard towards a long, low station. I hid in a linen cupboard. The train stopped. I heard voices, the whirring noises of unidentifiable machines inside the carriages, then nothing. I tried to get out of the cupboard but it had been locked from the outside. While I was sitting wondering what to do next, more voices sounded through the cupboard's metal door, and I formed the impression that the train was filling up with people. After a few hours, the train moved again. I slept in the locked cupboard that night and was discovered by a steward the next morning.

The train was full of passengers; well-dressed ladies and gentlemen who looked as though they came from the bridge. They wore summer suits and dresses; they sipped cocktails chinking with ice at little tables in the observation cars. They looked vaguely disgusted when they saw me led through the train in my crumpled, stale clothes, a railway policeman's hand forcing one of my arms painfully high up my back. Outside, the countryside was mountainous, full of tunnels and tall viaducts spanning boulder-torn torrents.

I was interrogated by one of the train's deputy firemen, a young man in a sparkling white uniform which seemed rather inappropriately spotless given his rank. He asked me how I came to be on board; I told the truth. I was taken back through the train and locked in a bare, barred section of a baggage car. I was fed well, on galley leftovers. My clothes were taken from me, washed and returned. The handkerchief Abberlaine Arrol had monogrammed, and on which she had left a smudged red image of her lips, came back quite thoroughly clean.

The train moved for days through mountains, and then across a high, grass-covered plain where distant herds of animals scattered and fled on its approach and the wind blew continually. Beyond the plain it started to climb towards another range of mountains. It unwound its way through those, across more spindly viaducts and long tunnels, descending all the time and stopping at small, quiet towns along the way, amongst forests and green lakes and rock spires plinthed in scree. The barred and rattling little cell had only a single small window two feet long and six inches high, but I could observe the scenery well enough, and the fresh, rarefied smells of the mountains and the plateaux leaked through the large baggage door at one end of the car, wrapping me with the scents which I seemed, tantalisingly, to recall from long ago.

I had other dreams, besides the recurring one of the man in the severely beautiful city; I dreamt one night that I woke up and went to my small window and looked out over a boulder-strewn plain, and saw two sets of weak lights as they approached each other over the moonlit wasteland. Just as they stopped, facing each other, the train roared into a tunnel. On another occasion I thought I looked out during the day, while the train ran along the top of a great cliff facing a blue, glittering sea; the cliff-edge was strung about with puffy clouds which we continually plunged into and rushed out of, and a few times in the clear spaces, through a haze of heat, far below on the surface of the sun-burnished sea, I thought I saw two ships of the line sailing alongside one another, the space between them filled with puffs of grey smoke and darting flames. But that was a day-dream.

They left me here eventually, after the mountains and the hills and tundra and another, lower, colder plain. Here is the Republic, a cold, concentric place once known, they say, as The Eye of God. It is reached, from the barren plain, by a long causeway which divides the waters of a huge grey inland sea. The sea is almost perfectly circular, and the large island at its centre is also very close to that same geometric shape. The first I saw of it was the wall; the grey sea wall skirted by low surf and topped by low towers. It seemed to stretch curving away for ever, vanishing in a haze of distant rain squalls. The train clattered through a long tunnel, over a deep moat of water and then another wall. Beyond lay the island and the Republic, a place of wheatfields and wind, low hills and grey buildings; it seemed at once rundown and full of energy, and those grey buildings gave way, every now and again, to immaculate palaces and temples of an obviously earlier age, perfectly restored but seemingly unused. And there was a graveyard, a cemetery miles to each side, packed with millions of identical white pillars spread geometrically across a green sea of grass.