Helix — Eric Brown

Five hundred years from its launch, the colony vessel Lovelock is deep into its sub-lightspeed journey, carrying four thousand humans in search of a habitable planet.When a series of explosions tear the ship apart, it, it is forced to land on the nearest possible location: a polar section of the Helix -- a vast, spiral construct of worlds, wound about a G-type sun.

While most of the colonists remain in coldsleep, the surviving crew members of the Lovelock must proceed up- spiral in search of a habitable section. On their expedition they encounter extraordinary landscapes and alien races, meet with conflict and assistance, and attempt to solve the epic mystery that surrounds the origin of the Helix.
Helix combines engrossing scientific mystery, high adventure, and a depth of moving characterisation, written by one of the true talents of the genre.