cave

我们在徒步旅行中发现了一个古老的洞穴。

We discovered an ancient ___cave during our hike.

我们探索了山侧的一个黑暗洞穴。

We explored a dark ___cave in the side of the mountain.

第二天我去参观了一个内部有蓝色湖泊的洞穴。

The next day I went to see a ___cave with a blue lake inside it.