Silo 16 was the place on Malcassairo from which the last of the humans launched a rocket on their journey to Utopia. The name suggests that there may have been more silos on the planet. Before the launch, it had served for what seems to have been a long time as a waiting area and "sanctuary" of sorts for humanity. The Futurekind, who hunted and apparently ate humans, were not allowed inside Silo 16. One method of verifying that entry was only given to humans was to examine the entrants' teeth, allowing the guards to look for the distinctive fangs of the Futurekind. Despite this, at least one Futurekind got into the Silo, delaying the launch of their rocket. (TV: Utopia)
When Malcassairo went nova, Silo 16 was presumably swallowed in the planetary explosion that followed the rocket's departure. (TV: Last of the Time Lords)