m. c. de marco: To invent new life and new civilizations...

Today’s Big Dumb Object (BDO) is a Bucky habitat, a skeletal arrangement of rotating-for-gravity O'Neill or McKendree cylinders into a larger structure. Bucky Habitats are classified as having either a triangular or hexagonal arrangement, and any other arrangement is called a Kepler habitat instead. (The rungworld is not a Kepler habitat because the sides of the ladder are not themselves habitats.)

It’s not clear who first invented the Bucky Habitat, nor is it clear whether any particular arrangement (say, a closed structure) is intended or required. Orion’s Arm mentions a Bucky Habitat in the shape of a Dyson sphere along the lines of the Hex, but larger, and also shows a much more complex Kepler habitat called Kepleria.

Bucky Habitats have not appeared in fiction outside of Orion’s Arm and the variant seen in Hex, but Isaac Arthur discusses them in, for example, this video, where he mentions another name for them: polyhedral habitats.