洞門還向 Which Side The Door Opens
這個山就是陷空山了?但不知他的洞門還向那邊開?」行者道:「我這條路且是走熟了,只是這個洞叫做個無底洞,周圍有三百餘里,妖精窠穴甚多。这个山就是陷空山了?但不知他的洞门还向那边开?」行者道:「我这条路且是走熟了,只是这个洞叫做个无底洞,周围有三百余里,妖精窠穴甚多。
逐句解 Line by line
Is this mountain the Mountain of the Empty Trap?
陷空山 is the mountain that sinks away into nothing, and it has been named repeatedly without anybody remarking on it. The Heavenly King is the first to ask, because he is the first person here who has not been in it.
Only I do not know which side his cave door opens on."
那 is nǎ, the questioning one — which side, not that side. This is the general's question and it is a perfectly professional one: he has arrived with an army and wants to know where the entrance is.
Pilgrim said, "I know this road well enough. Only the cave is called the Bottomless Cave. It runs three hundred lǐ and more round about, and the fiend has a great many burrows in it.
Pilgrim answers the question and then takes it apart. 無底洞 is the Bottomless Cave, and the name is the problem: there is a door, and knowing where the door is buys you nothing. 甚 is shèn here, meaning very, the reading it has carried at this same phrase earlier in the chapter.
The Heavenly King asks a soldier's question and gets an answer that makes his army beside the point. A door can be forced; a hundred and seventy kilometres of tunnel cannot be surrounded.
Pilgrim has been down there three times and knows exactly what the difficulty is. The novel has him state it plainly here so that the discovery a few passages on lands as luck rather than skill.