But still, nobody yet knows the true extent of this subterranean water world.

但仍旧无人知晓这个地下水世界究竟有多大。

The clue lies on the desert floor in these lines of holes which mark the course of the subterranean water ways.

答案就在沙漠底下，这些排成一线的坑坑洞洞，这就是地下水道的路线。