the Stanford Torus -- 10,000 people (and cats and dogs and gerbils and weasels and goldfish) in outer space with Earth-equivalent gravity
The interior of a Stanford Torus, a structure in outer space which rotates to generate artificial gravity equivalent to Earth gravity. Painting by Don Davis courtesy of NASA.
The Stanford Torus was the principal design considered by the 1975 NASA Summer Study, which was conducted in conjunction with Stanford University (and published as Space Settlements: A Design Study, NASA Publication SP-413). It consists of a torus or donut-shaped ring that is one mile in diameter, rotates once per minute to provide Earth-normal gravity on the inside of the outer ring, and which can house 10,000 people.