Tartarus is a space station and prison that orbits Mars. In order to retain maximum safety, all the cells are detachable cubes that connect with one another over the vacuum of space and the larger part of the station, ensuring that all prisoners behave or risk killing themselves. Any attempts to attack the station or attempt a breakout may very well risk their lives as well. It’s intended to hold the worst of the worst: people too dangerous to keep in conventional prisons, yet haven’t been selected for capital punishment by their own respective governments. It’s never been broken in the 238 years since it’s founding.

The cells themselves are specially designed for each prisoner based on their vulnerabilities. When someone is to be brought to the prison, they’re put in the cell beforehand and then attached with the others.