They walked along the gentle curve of their makeshift world, nestled in the fading light of the dying star. He could see the #torus walls in the distance, misty blurs of spidersteel that trapped the sky, cocooning them against the void. Only, there would be no butterfly.

torus (math)
: In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle.