Carpe Jugulum (Discworld 23)

It was... well, it had been a standing stone, Agnes thought, but now it was a lying stone. Lichen grew thickly all over it.

'The marker. Hard to get out again if you don't know about it,' said Nanny. 'Let's head for the mountains. Esme all wrapped up, Magrat? Little Esme, I mean.'

'She's asleep.'

'Yeah,' said Nanny, in what Agnes thought was an odd tone of voice. 'Just as well, really. Let's go. Oh, I thought we might need these...'

She fumbled in the bottomless storeroom of her knickerleg and produced a couple of pairs of socks so thick that they could have stood up by themselves.

'Lancre wool,' she said. 'Our Jason knits 'em of an evenin' and you know what strong fingers he's got. You could kick your way through a wall.'

The heather ripped fruitlessly at the wire-like wool as the women hurried over the moor. There was still a sun here, or at least a bright spot in the overcast, but darkness seemed to come up from beneath the ground.

Agnes... said Perdita's voice, in the privacy of her shared brain.

What? thought Agnes.

Nanny's worried about something to do with the baby and Granny. Have you noticed?

Agnes thought: I know Nanny keeps looking at little Esme as if she's trying to make up her mind about something, if that's what you mean.

Well, l think it's to do with Borrowing...

She thinks Granny's using the baby to keep an eye on us?

I don't know. But something's happening...

The roar ahead grew louder.

'There's a little stream, isn't there?' said Agnes.

'That's right,' said Nanny. 'Just here.'

The moor fell away. They stared into the abyss, which didn't stare back. It was huge. White water was just visible far below. Cold, damp air blew past their faces.

'That can't be right,' said Magrat. 'That's wider and deeper than Lancre Gorge!'

Agnes looked down into the mist. It's a couple of feet deep, Perdita told her. I can see every pebble.

'Perdita thinks it's a... well, an optical illusion,' Agnes said aloud.

'She could be right,' said Nanny. 'Gnarly ground, see? Bigger on the inside.'

Magrat picked up a rock and tossed it in. It bounced off the wall a few times, tumbling end over end, and then nothing was left but a stony echo. The river was too far down even to see the splash.

'It's very realistic, isn't it?' she said weakly.

'We could use the bridge,' said Nanny, pointing.

They regarded the bride. It had a certain negative quality. That is to say, while it was possible at the limits of probability that if they tried to cross the chasm by walking out over thin air this might just work  -  because of sudden updraughts, or air molecules suddenly all having a crazy idea at the same time  -  trying to do the same thing via

the bridge would dearly be laughable.

There was no mortar in it. The pillars had been piled up out of rocks laid like a drystone wall, and then a series of big flat stones dropped across the top. The result would have been called primitive even by people who were too primitive to have a word yet for 'primitive'. It creaked ominously in the wind. They could hear stone grind against stone.

'That's not right,' said Magrat. 'It wouldn't stand up to a gale.'

'It wouldn't stand up to a dead calm,' said Agnes. 'I don't think it's really real.'