'You have a choice,' said Indra, 'though I know which one you'll take. We can go up on an external elevator, and admire the view – or an interior one, and enjoy a meal and some light entertainment.'

'I can't imagine anyone wanting to stay inside.'

'You'd be surprised. It's too vertiginous for some people – especially visitors from down below. Even mountain climbers who say they've got a head for heights may start to turn green – when the heights are measured in thousands of kilometres, instead of metres.'

'I'll risk it,' Poole answered with a smile. 'I've been higher.'

When they had passed through a double set of airlocks in the exterior wall of the Tower (was it imagination, or did he feel a curious sense of disorientation then?) they entered what might have been the auditorium of a very small theatre. Rows of ten seats were banked up in five tiers: they all faced towards one of the huge picture windows which Poole still found disconcerting, as he could never quite forget the hundreds of tons of air pressure, striving to blast it out into space.

The dozen or so other passengers, who had probably never given the matter any thought, seemed perfectly at ease. They all smiled as they recognized him, nodded politely, then turned away to admire the view.

'Welcome to Skylounge,' said the inevitable autovoice. 'Ascent begins in five minutes. You will find refreshments and toilets on the lower floor.'

Just how long will this trip last? Poole wondered. We're going to travel over twenty thousand klicks, there and back: this will be like no elevator ride I've ever known on Earth...

While he was waiting for the ascent to begin, he enjoyed the stunning panorama laid out two thousand kilometres below. It was winter in the northern hemisphere, but the climate had indeed changed drastically, for there was little snow south of the Arctic Circle.