A party of climbers imported a Swiss guide into the Lake District, and on the first morning, surveying the misty peaks before him, he pointed to a ledge about two thirds of the way up one of them and suggested that the party should spend the night there. 

【翻译】一群登山者在一名瑞士导游的引导下进入了湖区，第一天早晨，他观察了面前雾蒙蒙的山峰，指着其中一座山在大约三分之二位置的一处岩石架，建议他们在那里过夜。

a ledge about two thirds of the way up one of them：

a ledge：岩石架，山上的凸出的平台。

about two thirds of the way：坡道长度的大约三分之二处。

up：沿着。up one of them 介词短语修饰 way。

one of them：其中一座山