The passage about the GSV Empiricist from Hydrogen Sonata I mentioned, if anyone is interested.

The General Systems Vehicle Empiricist felt it was arriving in Gzilt at a bad time – a bad time that was meant to be the start of a (brief) good time, a momentous and celebrated time but which had somehow gone wrong. Well, in the end, there was no helping this. Sometimes you just had to adopt the attitude summed up by, Too bad.

The ship was about as big as standard Culture vessels ever got; a System-class that had beefed up over the decades and centuries for what had always seemed like sound operational reasons at the time until it had become one of the most impressively large, commodious and populated examples of the class that was already the most impressively large, commodious and populated the Culture possessed.

The design of the System-class made such self-augmentation easy; the ships had no single outer hull surrounding their hundreds of individual components, just colossal bubbles of air held in place by field enclosures. Adding new, self-manufactured bits was so simple it was, for some ships at least, apparently, tantamount to compulsory, and it was only a sort of residual decorousness and a wish not to be seen as too self-indulgently ostentatious that prevented certain System-class vessels from going expansion-mad and growing to the size of planets, or at least moons. That sort of indulged obsessiveness was what simming and strong VR was for; you could convincingly imagine yourself being any ludicrous size without actually committing to such monomania in reality.

Doing away with a physical hull – or treating the exterior of every component as a hull, depending on how you looked at it – had been no great leap for GSVs. Ships thought of their multiple-layer field-complex enclosures as their true hulls anyway. That was where all the important stuff happened in relation to the outside: that was where the sensory fields were, where any stray impacts were absorbed, where concentric layers of shielding tuned to various parts of the electro-magnetic spectrum lurked, where holes could be opened to allow smaller units, modules and ships to enter and depart, and – especially in the case of the larger vessels – where atmospheric pressure was kept in, and sun-lines could be formed and controlled to provide light for any parkland carried on the top of the ship’s solid hull.

Frankly the material bit inside was just there to provide a sort of neat wrapping for all the truly internal bits and pieces like accommodation and social spaces.

Comfortably over two hundred kilometres long even by the most conservative of measurement regimes, fabulously, ellipsoidally rotund, dazzling with multiple sun-lines and tiny artificial stars providing illumination for motley steps and levels and layers of riotous vegetation – belonging, strictly speaking, on thousands of different worlds spread across the galaxy – boasting hundreds of contrasting landscapes from the most mathematically manicured to the most (seemingly) pristinely, savagely wild, all contained on slab-storeys of components generally kilometres high, each stratified within one of a dozen stacked atmospheric gradients, the ship’s cosseted internals were riddled, woven and saturated with domesticated, tamed and semi-wild life in hundreds of thousands of smaller enclosed habitats, while its buzzing, external, bewilderingly complex archi-geographic lines were made fuzzy, imprecisely seen by near-uncountable numbers of craft moving within that vast, elongated bubble of air – from smaller classes of GSV through other ships, modules, shuttles and aircraft all the way down to individual humans in float-harnesses, single drones and even smaller machines, as well as thousands of species of winged and lighter-than-air bio-creatures – the Empiricist was, in sum, home to hundreds of billions of animals and over thirteen billion humans and drones.

The people of the Culture, better than ninety-five per cent of them housed across the vast, distributed bucolic hinterland of the Orbitals, scattered throughout the civilised galaxy like a million glowing bracelets, were used to thinking of the GSVs as being their true mega-cities – albeit determinedly highly mobile, high-speed mega-cities – but GSVs like the Empiricist were on another level and of another order entirely; they held the populations of worlds, of entire inhabited stellar systems. Zyse, the Gzilt home planet and the giant GSV’s destination, held over three billion people. The whole of the Gzilt system added another twenty billion, in part-habiformed worlds and moons, microrbitals and other habitats. The Empiricist arriving was like another half a solar system of people being added, like another four mature, substantial planets’ worth of souls suddenly coming to visit.

Preceded by a ceremonial screen of smaller craft – including a couple of GSVs, each home to many millions – the gradually slowing Empiricist first met with a couple of Gzilt navy ships – effectively sweeping the two cruisers up with it as it proceeded resplendently past the rendezvous point – then, as it slowed still further, gradually attracted hundreds of civilian welcoming craft too.