you just need space. And whether its for a colony, mining base,
or interstellar spacecraft, what can beat a hollowed out asteroid?
Sure, it means shifting tens of millions of tons of rock ( or
worse, nickel/iron), adapting the interior for habitation, getting
water and oxygen from somewhere, stabilising the spin of the thing so
it doesn't precess all over the place, adding the thrusters just
right to move it to the stars or a more convenient orbit (all this
while wearing spacesuits, mind), and then hoping the whole thing
doesn't leak, but you wouldn't want to go for the more difficult
options, would you?