back to the salt mines
Saying that you have to go back to the salt mines is a humorous way of talking about returning to work, usually with some reluctance
Example : We get two days off at Christmas and then it’s back to the salt mines
back to square one
To say that someone is back to square one, means that they have not succeeded in what they were trying to do, and so they have to start again
Example : When the plans were refused, it was back to square one for the architect