刀山火海 [- shān huǒ hǎi] a mountain of swords and a sea of flames — most dangerous places; most severe trials; immense dangers and difficulties (比喻非常危险和困难的地方)：
•¶ 敢闯刀山火海 dare to climb a mountain of swords or plunge into a sea of flames; be ready to undergo the most severe trials