千里之遙 A Thousand Li To The South
行者道：「既知，一一說來。」土地道：「那妖精攝你師父去，在那正南下，離此有千里之遙。那廂有座山，喚做陷空山。行者道：「既知，一一说来。」土地道：「那妖精摄你师父去，在那正南下，离此有千里之遥。那厢有座山，唤做陷空山。
逐句解 Line by line
Pilgrim said, "Since you know, then out with it, every bit."
一一, one by one, is a fixed adverbial phrase, and both characters keep the citation tone yī rather than shifting as a running numeral would. Chapters 66 and 74 read it the same way.
The earth god said, "That fiend who carried off your master went away to the due south of here, a thousand lǐ distant.
那 is nà at both appearances, pointing. A Ming lǐ is about 576 metres, so a thousand of them is some 576 kilometres — and Pilgrim covers that in a fraction of one somersault.
There is a mountain over there, called the Mountain of Hollow Emptiness.
陷空山 — the mountain that sinks away into nothing. The name is the answer to the riddle-verse's earthen passage.
The intelligence arrives, and it is precise: due south, a thousand lǐ, a named mountain. Two minor gods have the answer the whole company lacked.
The distance is worth doing the arithmetic on. A thousand Ming lǐ is around 576 kilometres — a serious journey on foot and nothing at all to a creature whose single somersault covers a hundred and eight thousand of them.
The mountain's name is the chapter's last piece of foreshadowing paying off. The riddle-verse said she made an earthen passage her door and house. The place is called Hollow Emptiness, and what is in it has no bottom.