Every Culture habitat - whether it was an Orbital or other large structure, a ship, a Rock, or a planet - possessed Storage facilities. Storage was where some people went when they had reached a certain age, or if they had just grown tired of living. It was one of the choices that Culture humans faced towards the end of their artificially extended three-and-a-half to four centuries of life. They could opt for rejuvenation and/or complete immortality, they could become part of a group mind, they could simply die when the time came, they could transfer out of the Culture altogether, bravely accepting one of the open but essentially inscrutable invitations left by certain Elder civilisations, or they could go into Storage, with whatever revival criterion they desired.

Some people slept for - say - a hundred years at a time then lived a single day before returning to their undreaming, unageing slumbers, some wanted simply to be woken after a set time had passed to see what had changed while they’d been gone, some desired to come back when something especially interesting was happening (content to leave that judgement to others), and some only wanted to be brought back if and when the Culture finally became one of the Elders itself.

That was a decision the Culture had been putting off for many millennia; in theory it could have sublimed anything up to eight thousand years ago, but - while individuals and small groups of people and Minds did sublime all the time, and other parts of the society had hived off and split away, to make their own decisions on the matter - the bulk of the Culture had chosen not to, determining instead to surf a line across the ever-breaking wave of galactic life continuation.

Partly it was a kind of curiosity that no doubt seemed childish to any sublimed species; a feeling that there was still more to discover in base reality, even if its laws and rules were all perfectly known (and besides, what of other galaxies, what of other universes? Did the Elders have access to these but none of them had ever seen fit to communicate the truth to the unsublimed? Or did all such considerations simply cease to matter, post-sublimation?).

Partly it was an expression of the Culture’s extrovertly concerned morality; the sublimed Elders, become as gods to all intents and purposes, seemed to be derelict in the duties which the more naive and less developed societies they left behind ascribed to such entities. With certain very limited exceptions, the Elder species subsequently took almost nothing to do with the rest of life in the galaxy whose physical trappings they invariably left behind; tyrants went unchecked, hegemonies went unchallenged, genocides went unstopped and whole nascent civilisations were snuffed out just because their planet suffered a comet-strike or happened to be too near a super-nova, even though these events occurred under the metaphorical noses of the sublimed ones.