salt mine

You can refer to any repetitive, difficult job or task as a salt mine. If your mom groans, "Off to the salt mine" as she leaves for work, she probably doesn't love her job.

The literal definition of salt mine — a mine where salt is extracted — explains the origin of the figurative meaning. Work in a salt mine is physically challenging and monotonous, and any job that feels that tedious can be called a salt mine. People sometimes use the term in a more lighthearted or joking way: "It was a great weekend, but tomorrow it's back to the salt mine."