A bathroom addition in the basement required a lot of concrete cutting, and the state of the existing cast iron pipe necessitated a full redo. This is a lot of work but not a place to cut any corners and is much easier to do with the walls fully exposed, basically at this stage the work is like new construction.
the iron pipe was all torn out and replaced by abs, much easier to work with and not issue of covering the walls with new drywall only to find the old plumbing was faulty.
new bathroom is installed and passed inspection. The old slab is cut and smashed out to allow room to get the bathroom drain network graded back to the main stack. A wet bar added required a further 10 ft of trench. Along with the new windows cored into the walls (3x) this is a radical basement transformation.