noun · A figurative expression for a daunting challenge or a severe trial that is difficult to overcome.

只要我们齐心协力，就没有过不去的火焰山。

noun · The legendary mountain from the novel Journey to the West or the actual mountain range in the Turpan depression of Xinjiang.

吐鲁番的火焰山是中国夏季最热的地方之一。