Ceres is a bustling port within the belt and a commercial, entertainment, and economic hub dealing with the markets of both the inner and outer planets. Ceres is home to the largest colonies in all of the belt. But Ceres is also home to the rather infamous penal colony: Lono
Lono is a massive bore hole dug around the crater which it gets it's name. It is currently managed by the Prometheus corporation as a penal facility for criminals within the belt or nearby colonies. Lono would stretch for roughly 2 miles at its current depth and would keep slowly expanding for years to come. The colony itself is dug into the walls of the bore holes with workshops, repairbays, and food services being on large elevators that are periodically lowered further into the hole.
What would make such a project economically viable? Would, for example, the silicate in such massive quantities be worth it or should Prometheus focus on maybe ores, or tholins?
Labor is cheap due to both robotics and subsides being paid by the Hegemony to use lono as a penal facility for criminals within the belt.
The bore hole itself has particle uses later on with the possibility of a O'Neil cylinder being placed inside once the mine dries up or isn't economically viable. Something Prometheus has already done on Eros.
Most of the equipment is fuelled by either tholins or hydrogen fusion via water rumored to be within Ceres (if they discover that there isn't water Ice will do)