n(山，窑)洞(large natural hollow in the side of a cliff or hill，or under the ground with an opening to the outside)[C]：Bears often hibernate in～s.熊常常在山洞中冬眠。The children explored the～.孩子们在山洞中探险。

v 探洞(explore caves as a sport)(通常用于go caving短语中)[I]：He likes～ing.他喜欢到山洞去探奇。

cave in (v adv)(使)塌陷(vi & vt)：The roof of the house/mine/tunnel～d in.房屋/矿井/通道的顶子塌陷了。The ceiling/ground～d in (on them).天棚/地面塌陷(压在他们身上)了。My whole world is～ing in on me.(fig)我的天整个塌下来了。The flood～d in the banks of the river.洪水冲决了河堤。