Location from remembrance-of-earths-past by
The string of O'Neill-cylinder space cities humanity built in the gravitational shadows of Jupiter and Saturn during the Bunker Era — humanity's last addressable home before the dual-vector foil, intended as cover from a strike that never came from where they expected.
Bunker World is the architecture of false safety. The species spent decades building cities to hide behind Jupiter from a Dark Forest strike that, when it came, did not care about Jupiter. The dual-vector foil flattens 3D into 2D and Jupiter is no shield against geometry. Most of humanity dies here in the last act, including the cities Cheng Xin walks through on her last visit before Halo carries her out of the system.
Long rotating cylinders kilometers in diameter, painted dull gray on the outside and lined with green farmland and cities along the inner curve. Strung in cluster formations along the L-points of Jupiter and Saturn, hidden from sunward observation by the gas giants' bulk. Inside one of them — Asia I — looks like a folded continent on the inside of a tube.