1. The fort on top of the steep hill is inaccessible.
    很难接近陡峭山顶上的堡垒。

2. As by falling into inaccessible caves, or into an ice crevasse,
    如掉进难以到达的洞穴，或掉进冰河裂缝里，

3. In this much-travelled world, there are still thousands of places which are inaccessible to tourists.
    在这个旅游频繁的世界上，仍有成千上万个游人足迹未至的地方。