We walked for two and a half hours to get there—first up a mountain to a ridge from where we had fantastic views and then down a steep path to the valley below.

这里面from where引导定语从句是什么用法？

一般定语从句是“介词+关系代词which/whom”,from where是怎么回事？

解答如下：

这里介词(from)+关系副词(where)相当于from +地点状语，即关系副词相当于代替前面的一个介词短语，以便所表达地点更加具体，更加清晰准确。

A: from which 中的关系代词which只能代替”一个表示地点/事物的名词，不能代替一个介词短语，有时候无法准确表达一个确切地点状语。

B:from where 中的关系副词where能代替一个“表示确切地点的介词短语”因此能描述一个比较准确地点状语。这个比较准确地点状语是用来说明定语从句谓语动作发生的地点。（即某人在某地干了某事）

(备注，还可以把介词短语当作一个“there”的地点状语来理解，即from where=from there)

【1】Soon after getting off his horse, the captain appeared at the second storey windows, from where he could see nothing but trees.

=Soon after getting off his horse, the captain appeared at the second storey windows,and from at the second storey windows he could see nothing but trees.

下马不久，上尉就出现在二楼的窗口了。他从那里除了树木什么也没看到。(引导定语从句)

划线部分相当于…

A: and from at the second storey windows.

【2】She climbed up to the top of the hill, from where she could have a good view of the whole town.(非限制性定语从句）

=She climbed up to the top of the hill, and from on the top of the hill she could have a good view of the whole town.（有连词and 连接并列句）

=She climbed up to the top of the hill, from on the top of which she could have a good view of the whole town.(非限制性定语从句）

她登上山顶，从那里她可以一览全城风光。（引导定语从句）

划线部分相当于

A:and from on the top of the hill

B:from on the top of which(which代替先行词the hill)

【3】He hid himself in a tree, from where he could see the enemy in the distance.

他躲在一棵树上，从那儿他可以看到远处的敌人。

【4】We went up to the roof, from where we had a good view of the procession. 

爬上屋顶，从那儿可以很好地观看游行。

【5】He hid himself under the bed, from where he could hear what they were talking. 

=He hid himself under the bed and from under the bed he could hear what they were talking.

他躲在床下面，他可以从床下听到他们谈话。

（解析：句中的 from where 可理解为 from under the bed，意思是“从床下面”,即在定语从句中关系副词where取代/代替了介词短语under the bed）

注意和下面第4个句子区别

【4】He hid himself under the bed,where he could hear what they were talking. 他躲在床下面，在床那儿他听到他们谈话。

（解析：句中的 where 可指为“在床边”“在床上”“在床下”等，意思不够。意思比较模糊）

为了让你有更好理解，现补充下面内容

特殊引导词“from where”引导定语从句

(1)Where are you from？

(2)Where do you come from?

from这个介词比较特殊，其后可以再加上一个介词短语。

A:from under the table 从桌子底下

B:from behind the door 从门后面

Look over there! some people are standing under the big tree,___ you can enjoy the whole view. 

A.where  B.from which  C where D from where

【D答案解析】where 代表 under the tree 这个地方，如果用 which 就只能代表the big tree, 这句话的意思不是Enjoy the whole view from the big tree而是from under the big tree.所以只能用D from where。

【最后总结】

当先行词为：介词+地点名词而不是单个地点名词作先行词时，定语从句需要使用引导词from where 来引导定语从句。

1.在from which 中，which指代的是前面的某个名词或代词。如：

The village has only one well from which the villagers draw water. 这个村子仅有一口井供村民们取水。

This is the point, from which all distances can be measured. 就是这个点，从这个点，各方面的距离都可以测量。

2.在from where中，where指代的是前面表地点的介词短语，指明具体的地点方位。如：

He hid himself under the bed, from where he could hear what they were talking about. 他躲在床下面，从床下他可以听到他们在谈些什么。(from where = and from under the bed)

3.一般情况下，where可直接引导定语从句。

What is the name of the town where we stayed last night? 我们昨晚呆过的那个小镇叫什么？

4.但在特定语境中，用where不如用from where。如：

She climbed up to the top of the hill, from where she could have a good view of the whole town. 她登上山顶，从那里她可以一览全城风光。

该句中的from where相当于and from on the top of the hill或from on the top of which…, 不可变为from which，但可直接用where引导。不过，语义较为含糊，不如from where生动、形象、具体。where常笼统地表示位置，所含的意义很泛，它可以指“不同方位的介词+地点/位置名词”，这些常见的方位介词有 in, on, by, at, below, under, beside, inside, above, near...等等。

【补充】

英语语法网上还有一篇文章，或许对你有所帮助。

http://www.yygrammar.com/Article/201104/2154.html