It takes place in the neighboring cities of Diaspar and Lys on Earth a billion years in the future. They are the only inhabitants of Earth, the Solar system and galaxy. Out of fear of some invaders, they gave up and completely forgot travelling into space or even outside their city.
Both cities are completely separated and developed different cultures: Diaspar depending on machines, Lys on nature. Diaspar inhabitants live forever and are kind of recycled only to return after some 100,000 years in a new body, whereas Lys inhabitants live for short time spans but mastered telepathy.
The novel follows the mystery of one Diaspar man Alvin who learns about his special role: He is the first one to be able to get outside of the city and explore its surroundings and the whereabouts of humanity.
First half is description heavy – nearly no action or dialogues at all, reflecting the insular conversatism and setting the atmosphere of Diaspar in a very good way. In the second half, Alvin’s quest is narrated through a bit more action and dialogues, and he even gets a somewhat shallow sidekick from Lys. I’d say it reads far more pulpish than the first half which I found better.
The work is quite old – from 1956 – but in contrast to many classic SF titles it aged very well: You’ll find no ridiculous artefacts concerning computers, phones, cars or similar items that the authors weren’t able to extrapolate correctly. Instead, you can even get a glimpse on relatively new innovations like MMORPGs called „adventures“ in the novel.
Clarke explores isolationism of neighboring cultures and how to break them up, which you’ll find very modern. He touches utopian versions of perilous growth versus survival.
On the negative side, I didn’t like the notions of telepathy, disembodied intelligence – I generally don’t need them included in SF. Additionally, I didn’t need the mentioning of „1000 of million years“ nearly every odd page and the accompanying gigantomanism.
Character development – especially of Alvin – was homeopathic, if existent at all.
I liked the novel but wouldn’t consider it as his best work.