Usually, salt mines. a place of habitual confinement and drudgery:
After two weeks of vacation it will be back to the salt mines for the staff.
Origin
1675-85
salt mines in Technology
Dense quarters housing large numbers of programmers working long hours on grungy projects, with some hope of seeing the end of the tunnel in N years. Noted for their absence of sunshine. Compare playpen, sandbox. [Jargon File]