mountain of difficult problems; pile of thorny issues
Idiomatic expression describing a situation where many difficult problems have accumulated, like a mountain. Often used in political, business, or organizational contexts.
The new cabinet started with a mountain of difficult problems.
This project is a pile of thorny issues, and I don't know where to start.
Means 'pile up like a mountain' and is used in compounds like 難問山積 or 課題山積. 難問山積 is a specific idiomatic compound emphasizing difficult problems.
Similar meaning but uses the more general 問題 (problems) instead of 難問 (difficult problems). 難問山積 stresses the severity of the issues.
A four-character compound (yojijukugo) combining 難問 (difficult problem) and 山積 (pile up like a mountain). The exact origin is uncertain, but it follows a common pattern of metaphorical compounds in Japanese.