salt mine

Short definition from Wiktionary

Noun

1. 1
   Any mine used for the extraction of salt.
2. 2
   Any laborious work situation, especially in a confined space.
3. 3
   An abundance of indignation felt by one person or a group of people due to over-sensitivity, humourlessness, disappointment, or defeat; a gold mine (sense 3) of salt (noun sense 11).