刀山火海

dāoshānhuǒhǎi
  1. lit. mountains of daggers and seas of flames
  2. fig. extreme danger (idiom)

CEDICT

mountains of daggers and seas of flames; (figurative) extreme danger

Wiktionary

比喻非常危险和困难的地方。如：「为了正义公理，就算是刀山火海，我也绝不退缩。」也作「火海刀山」。

重編國語辭典

Entry Composition

1 刀 dāo
  1. (slang) (loanword) dollar
  2. classifier for sets of one hundred sheets (of paper)
  3. classifier for knife cuts or stabs
  4. (Internet slang) to bargain; to ask for a small discount (esp. on second-hand marketplaces)

classifier: 把
2 山火 shānhuǒ
  1. wildfire
  2. forest fire
3 海 hǎi
  1. ocean
  2. sea
  3. great number of people or things
  4. (dialect) numerous

classifiers: 個, 片