行军篇 NO.3：

凡地有绝涧、天井、天牢、天罗、天陷、天隙，必亟去之，勿近也。
吾远之，敌近之；吾迎之，敌背之。
军旁有险阻、潢井、葭苇、林木、翳荟者，必谨覆索之，此伏奸之所处也。

这句啥意思：

凡遇到或通过“绝涧”、“天井”、“天牢”、“天罗”、“天陷”、“天隙”这几种地形，必须迅速离开，不要接近。
我们应该远离这些地形，而让敌人去靠近它；我们应面向这些地形，而让敌人去背靠它。
军队两旁遇到有险峻的隘路、湖沼、水网、芦苇、山林和草木茂盛的地方，必须谨慎地反复搜索，这些都是敌人可能埋设伏兵和隐伏奸细的地方。

英文这么说：

Country in which there are precipitous cliffs with torrents running between, deep natural hollows,confined places, tangled thickets, quagmires and crevasses,should be left with all possible speed and not approached.
While we keep away from such places, we should get the enemy to approach them; while we face them,we should let the enemy have them on his rear.
If in the neighborhood of your camp there should be any hilly country, ponds surrounded by aquatic grass,hollow basins filled with reeds, or woods with thick undergrowth, they must be carefully routed out and searched;for these are places where men in ambush or insidious spies are likely to be lurking.

几种地形的白话分析

绝涧：溪谷深峻，水流其间；天井：类似于盆地； 天牢：高山环绕，易进难出；天罗：草深林密，难以出入；天陷：地势低洼，道路泥泞； 天隙：两山相向，涧道狭窄。