Artwork of a Bernal Sphere that could house 10,000 people, courtesy of NASA Ames Research Center. This method of building space colonies was proposed in Bernal’s 1929 The World, the Flesh & the Devil: An Enquiry into the Future of the Three Enemies of the Rational Soul (Chapter 2: The World):
Imagine a spherical shell ten miles or so in diameter, made of the lightest materials and mostly hollow…The globe would fulfil all the functions by which our earth manages to support life. In default of a gravitational field it has, perforce, to keep its atmosphere and the greater portion of its life inside; but as all its nourishment comes in the form of energy through its outer surface it would be forced to resemble on the whole an enormously complicated single-celled plant.
More on Bernal Spheres here (NSS) and here (Space Anthropology).