The main problem for engineers was the location of underground rivers in the area.

【location】工程师们面对的主要问题在于确定该地区地下河的位置。

But then once inside, you can start exploring the massive cave system which measures over 143 miles and is part of the world's largest underground river.

一旦你进去了，你就可以开始探索超过 143 英里的巨大洞穴系统，它们是世界上最大的地下河系统的一部分。

Here, the magma forms pockets and veins in the ground, heating underground rivers and pools to temperatures reaching 300 degrees.

在这里，岩浆在地下形成气穴和矿脉，将地下河流和水池加热至 300 度的温度。

Within tens of square Kilometers, there are more than 600 sinkholes and floor drains, a huge underground river, and rolling mountain meadows, which combine to form a primitive and beautiful natural scenery.

数十平方公里的范围内又六百多个天坑地漏流量巨大的地下暗河与连绵起伏的高山草甸组合成了原始而幽美的自然风光。

Since the limestone upon which everything around here sits is easily dissolved by water, the Karst is honeycombed with a vast network of caves and underground rivers.

由于这里周围一切所处的石灰岩很容易被水溶解，喀斯特地貌呈蜂巢状， 拥有巨大的洞穴和地下河网络。

The waterfall is part of an aqueduct -- a man-made, underground river carved out of the rock -- allowing freshwater to flow 15 miles from a mountain spring into the city.

瀑布是渡槽的一部分 - 一条从岩石中开凿出来的人造地下河 - 使淡水从山泉流入城市 15 英里。

It used to be an underground lake or an underground river, but that water moved on to some other place, leaving behind or having already cut this cave in the rock, right?

本来是个地下湖或者地下河，但是那个水流到别的地方去了， 留下或者已经把这个岩洞给挖出来了吧？