Heaven's River is the name that the Quinlans use for the megastructure that is their home.
Updated depiction of Heaven's River, with Patrol Ship and Heaven-5 vessel by M.W.F. Baily. Image revised to more closely portray view when close enough to see individual strands.
It is a topopolis type of construction, encircling Eta Leporis in an orbit between EL 2 and EL 3. Both of these planets are in the habitable zone of the star. The Bobs theorize that there was a third habitable planet in the star's comfort zone, and that the builders of Heaven's River dismantled the planet and used its raw materials to build the megastructure.
Eta Leporis 2, which the natives call Quin, was once habitable, but global warfare has left it a wasteland. It is a dead planet, with an atmosphere and large landmasses with many rivers. However, the rivers are polluted and clogged with debris. The land is pockmarked by craters caused by bombs, nukes, and small asteroids.
At some point near the end of the global war, the Quinlans built the topopolis and evacuated the survivors of Quin to the megastructure.
Artistic impression of the Heaven's River topopolis and patrol ship by M.W.F. Baily. Structure is exaggerated to convey the concept.
The structure is a torus knot that wraps around the star three times with strands that wind around each other, for a total length of a billion miles.
There is an external shell and an internal shell, separated by large bearings. The inner shell rotates at about 1950 miles per hour, producing the same g-forces (.86g) as on Quin.
There are three external docking ports on each of the three strands, for a total of nine docks. They are used by Boojums, planetary defense drones controlled by AMI.
The cylinder has a radius of 56 miles. There is a central tube that runs down the middle of the cylinder. An artificial sun travels along the tube. It also generates a hologram of the sky, so no matter where an observer stands, when they look up they don’t see the other side of the cylinder, but rather they see an image of the sky. The artificial sun travels down the cylinder at the same rate as the rotation of Quin. Each segment is 526 miles long, because that is the distance the artificial sun travels in one Quin day.
The segments are separated by a mountain range. The range is hollow and the rocks are made of an artificial, lightweight, pumice-like material. Inside the mountain ranges are four spokes that support the central tube, that provide structural stability for the inner cylinder, and that contain key infrastructure. There is an elevator running the length of each spoke, leading from the base of the mountains at the cylinder’s edge to the peak of the mountains at the central axis.
Four river systems run the length of it: Arcadia, Paradise, Utopia, and Nirvana. Each major river has several tributaries throughout the topopolis, with interconnected waterways allowing boats or swimmers to transition from one major river to another. Each river passes through the mountain ranges that divide each section of the megastructure. Two of the rivers flow in one direction, and the other two flow in the opposite direction, making it possible to travel the length of a segment on one river and return to the starting point by switching rivers.
The ecosystem includes life forms from Quin, including birds, beasts of burden called howns, a deer analogue, a nocturnal wolf analogue called a larouche, and insects with radial symmetry (instead of the bilateral symmetry seen in Terran insects).
The rail system includes local trains as well as an express train that can traverse half of the topopolis in 12 days. The trains run in vacuum tubes along the inner shell of the megastructure, and spiral in a helix.