Cradle’s main defect had been a lack of simulated gravity, which had obliged those early generations to construct what amounted to glorified merry-go-rounds on which children could take turns being centrifuged in order to foster bone growth. Subsequent habitats—spinning tori mounted to the walls of the cleft—had actually been more crowded and confined than Izzy itself, and many generations had lived cramped lives in them with only occasional opportunities for R & R in Cradle’s sunny open volumes. In time they had learned to make bigger and better habitats, and Cradle had been abandoned for many centuries, an occasional destination for historians or curiosity seekers.