Two questions open the poem, and neither gets an answer: where have we ended up, and what is this high, rough peak? The speaker sounds a little lost, as if they've climbed somewhere unfamiliar and are only now looking around. The plural "we" makes it feel shared, though the poem never says who is included.
Then the tone shifts. The speaker mentions a book that holds "a secret door to the night," and the title, "Escape route," suggests that reading is the way out. The final line, "I will fall up," is the surprise. Falling normally means losing control, but here it points toward the sky, so fear turns into release. Judging by the imagery, the peak may be the place the speaker is stuck, and the book offers a way off it that goes up rather than down.
The mood is hushed and dreamlike, uneasy at first but ending in quiet, almost playful freedom.