I am now reminded
of 'Eon' by Greg Bear.
Which is pointless telling you if you have not read it because it's been about 10 years since I read it so can't explain it.
Suffice to say there is a big hollow rock in space, with colonists.
(
Pasanonic 's been known to cause insanity in laboratory mice,
Tue 3 Mar 2009, 10:58,
archived)