Rendezvous with Rama

Arthur C. Clarke's novel is set in the 2130s, when an object entering the Solar System turns out to be a perfectly smooth cylinder 50 kilometres long and 20 across, a sign that intelligent beings built it, and is named Rama. The object had been picked up by Spaceguard, a tracking system set up after an asteroid destroyed several cities in northern Italy decades earlier. Endeavour, the only ship close enough, is sent to intercept it, and the story follows its crew as they set out to learn what Rama is. Published in 1973, the novel won the Hugo, Nebula and Locus awards.

Andrej Karpathy called it a really fun alien contact mystery that kept him reading, and said he refuses to acknowledge its sequels.