This is where the dragons went.
They lie . . .
Not dead, not asleep. Not waiting, because waiting implies expectation. Possibly the word we're looking for here is. . .
. . . dormant.
And although the space they occupy isn't like normal space, nevertheless they are packed in tightly. Not a cubic inch there but is filled by a claw, a talon, a scale, the tip of a tail, so the effect is like one of those trick drawings and your eyeballs eventually realise that the space between each dragon is, in fact, another dragon:
They could put you in mind of a can of sardines, if you thought sardines were huge and scaly and proud and arrogant.
And presumably, somewhere, there's the key.
In another space entirely, it was early morning in Ankh-Morpork, oldest and greatest and grubbiest of cities. A thin drizzle dripped from the grey sky and punctuated the river mist that coiled among the streets. Rats of various species went about their nocturnal occasions. Under night's damp cloak assassins assassinated, thieves thieved, hussies hustled. And so on. And drunken Captain Vimes of the Night Watch staggered slowly down the street, folded gently into the gutter outside the Watch House and lay there while, above him, strange letters made of light sizzled in the damp and changed colour . . .
The city wasa, wasa, wasa wossname. Thing. Woman. Thass what it was. Woman. Roaring, ancient, centuries old. Strung you along, let you fall in thingy, love, with her, then kicked you inna, inna, thingy. Thingy, in your mouth. Tongue. Tonsils. Teeth. That's what it, she, did. She wasa . . . thing, you know, lady dog. Puppy. Hen. Bitch. And then you hated her and, and just when you thought you'd got her, it, out of your, your, whatever, then she opened her great booming rotten heart to you, caught you off bal, bal, bal, thing. Ance. Yeah. Thassit. Never knew where where you stood. Lay. Only thing you were sure of, you couldn't let her go. Because, because she was yours, all you had, even in her gutters . . .
Damp darkness shrouded the venerable buildings of Unseen University, premier college of wizardry. The only light was a faint octarine flicker from the tiny windows of the new High Energy Magic building, where keen-edged minds were probing the very fabric of the universe, whether it liked it or not.
And there was light, of course, in the Library.
The Library was the greatest assemblage of magical texts anywhere in the multiverse. Thousands of volumes of occult lore weighted its shelves.
It was said that, since vast amounts of magic can seriously distort the mundane world, the Library did not obey the normal rules of space and time. It was said that it went on forever. It was said that you could wander for days among the distant shelves, that there were lost tribes of research students somewhere in there, that strange things lurked in forgotten alcoves and were preyed on by other things that were even stranger. 
Wise students in search of more distant volumes took care to leave chalk marks on the shelves as they roamed deeper into the fusty darkness, and told friends to come looking for them if they weren't back by supper.
And, because magic can only loosely be bound, the Library books themselves were more than mere pulped wood and paper.
Raw magic crackled from their spines, earthing itself harmlessly in the copper rails nailed to every shelf for that very purpose. Faint traceries of blue fire crawled across the bookcases and there was a sound, a papery whispering, such as might come from a colony of roosting starlings. In the silence of the night the books talked to one another.
There was also the sound of someone snoring.
The light from the shelves didn't so much illuminate as highlight the darkness, but by its violet flicker a watcher might just have identified an ancient and battered desk right under the central dome.
The snoring was coming from underneath it, where a piece of tattered blanket barely covered what looked like a heap of sandbags but was in fact an adult male orangutan.
It was the Librarian.
Not many people these days remarked upon the fact that he was an ape. The change had been brought about by a magical accident, always a possibility where so many powerful books are kept together, and he was considered to have got off lightly. After all, he was still basically the same shape. And he had been allowed to keep his job, which he was rather good at, although 'allowed' is not really the right word. It was the way he could roll his upper lip back to reveal more incredibly yellow teeth than any other mouth the University Council had ever seen before that somehow made sure the matter was never really raised.
But now there was another sound, the alien sound of a door creaking open. Footsteps padded across the floor and disappeared amongst the clustering shelves. The books rustled indignantly, and some of the larger grimoires rattled their chains.
In the embrace of his gutter, half a mile away, Captain Vimes of the Night Watch opened his mouth and started to sing.
Now a black-robed figure scurried through the midnight streets, ducking from doorway to doorway, and reached a grim and forbidding portal. No mere doorway got that grim without effort, one felt. It looked as though the architect had been called in and given specific instructions. We want something eldritch in dark oak, he'd been told. So put an unpleasant gargoyle thing over the archway, give it a slam like the footfall of a giant and make it clear to everyone, in fact, that this isn't the kind of door that goes 'ding-dong' when you press the bell.
The figure rapped a complex code on the dark woodwork. A tiny barred hatch opened and one suspicious eye peered out.
“ 'The significant owl hoots in the night,' ” said the visitor, trying to wring the rainwater out of its robe.
“ 'Yet many grey lords go sadly to the masterless men,' ” intoned a voice on the other side of the grille.
“ 'Hooray, horray for the spinster's sister's daughter,' ” countered the dripping figure.
“ 'To the axeman, all supplicants are the same height. ' ”
“ 'Yet verily, the rose is within the thorn. ' ”
“ 'The good mother makes bean soup for the errant boy,' ” said the voice behind the door.
There was a pause, broken only by the sound of the rain. Then the visitor said, “What?”
“ 'The good mother makes bean soup for the errant boy. ' ”
There was another, longer pause. Then the damp figure said, “Are you sure the ill-built tower doesn't tremble mightily at a butterfly's passage?”
“Nope. Bean soup it is. I'm sorry. ”
The rain hissed down relentlessly in the embarrassed silence.
“What about the caged whale?” said the soaking visitor, trying to squeeze into what little shelter the dread portal offered.
“What about it?”
“It should know nothing of the mighty deeps, if you must know. ”
“Oh, the caged whale. You want the Elucidated Brethren of the Ebon Night. Three doors down. ”
“Who're you, then?”
“We're the Illuminated and Ancient Brethren of Ee. ”
"I thought you met over in Treacle Street,'' said the damp man, after a while.
“Yeah, well. You know how it is. The fretwork club have the room Tuesdays. There was a bit of a mix-up. ”
“Oh? Well, thanks anyway. ”
“My pleasure. ” The little door slammed shut.
The robed figure glared at it for a moment, and then splashed further down the street. There was indeed another portal there. The builder hadn't bothered to change the design much.
He knocked. The little barred hatch shot back.
“Look, 'The significant owl hoots in the night', all right?�
“ 'Yet many grey lords go sadly to the masterless men. ' ”
“ 'Hooray, horray for the spinster's sister's daughter', okay?' ”
“ 'To the axeman, all supplicants are the same height. ' ”
“ 'Yet verily, the rose is within the thorn. ' It's pissing down out here. You do know that, don't you?”
“Yes,” said the voice, in the tones of one who indeed does know it, and is not the one standing in it.
The visitor sighed.
“ 'The caged whale knows nothing of the mighty deeps,' ” he said. “If it makes you any happier. ”
“ 'The ill-built tower trembles mightily at a butterfly's passage. ' ”
The supplicant grabbed the bars of the window, pulled himself up to it, and hissed: “Now let us in, I'm soaked. ”
There was another damp pause.
“These deeps . . . did you say mighty or nightly?”
“Mighty, I said. Mighty deeps. On account of being, you know, deep. It's me, Brother Fingers. ”
“It sounded like nightly to me,” said the invisible doorkeeper cautiously.
“Look, do you want the bloody book or not? I don't have to do this. I could be at home in bed. ”
“You sure it was mighty?”
“Listen, I know how deep the bloody deeps are all right,” said Brother Fingers urgently. “I knew how mighty they were when you were a perishing neophyte. Now will you open this door?”
“Well . . . all right. ”
There was the sound of bolts sliding back. Then the voice said, “Would you mind giving it a push? The Door of Knowledge Through Which the Untutored May Not Pass sticks something wicked in the damp. ”
Brother Fingers put his shoulder to it, forced his way through, gave Brother Doorkeeper a dirty look, and hurried within.
The others were waiting for him in the Inner Sanctum, standing around with the sheepish air of people not normally accustomed to wearing sinister hooded black robes. The Supreme Grand Master nodded at him.
“Brother Fingers, isn't it?”
“Yes, Supreme Grand Master. ”
“Do you have that which you were sent to get?”
Brother Fingers pulled a package from under his robe.
“Just where I said it would be,” he said. “No problem. ”
“Well done, Brother Fingers. ”
“Thank you, Supreme Grand Master. ”
The Supreme Grand Master rapped his gavel for attention. The room shuffled into some sort of circle.
“I call the Unique and Supreme Lodge of the Elucidated Brethren to order,” he intoned. “Is the Door of Knowledge sealed fast against heretics and knowlessmen?”
“Stuck solid,” said Brother Doorkeeper. “It's the damp. I'll bring my plane in next week, soon have it-”
“All right, all right,” said the Supreme Grand Master testily. “Just a yes would have done. Is the triple circle well and truly traced? Art all here who Art Here? And it be well for an knowlessman that he should not be here, for he would be taken from this place and his gaskin slit, his moules shown to the four winds, his welchet torn asunder with many hooks and his figgin placed upon a spike yes what is it?”
“Sorry, did you say Elucidated Brethren?”
The Supreme Grand Master glared at the solitary figure with its hand up.
“Yea, the Elucidated Brethren, guardian of the sacred knowledge since a time no man may wot of-”
“Last February,” said Brother Doorkeeper helpfully. The Supreme Grand Master felt that Brother Doorkeeper had never really got the hang of things.
“Sorry. Sorry. Sorry,” said the worried figure. “Wrong society, I'm afraid. Must have taken a wrong turning. I'll just be going, if you'll excuse me . . . ”