Space Stations

Though it's clear that older space stations were often spinning toroidal tubes, the majority of inhabited stations settled on a more efficient design. Start with an asteroid several kilometers across and hollow out the interior (it's unknown whether this was done by construction crews or robots). Once hollowed, seal it, spin it, fill it. The resulting station is like a small planet turned inside out. Generally a fusion tube runs through the axis of the station, providing both power and light.