Where and when, either as interrogatives or as relatives, are not pronouns but pro-adverbs—they ‘stand for’ adverbials of place and time, respectively.
The place where I found it = the place at/in which I found it
Where did you find it? = At/in what place did you find it?
The time when I found it = the time at which I found it
When did you find it? = At what time did you find it?
It is thus not strictly true to say that “a relative clause always contains a relative pronoun”—it may also be headed by a relative pro-adverb. And in some cases (as in He told me to stop, which I did) the relative ‘pronoun’ is actually a component of a relative pro-verbal construction with DO.
- That's the shop which sells elephants.
- This is an elephant which the shop sold ____ .
In these sentences, the relative clauses have been marked out in bold. Each relative clause is like a small sentence inside the bigger sentence. In these relative clauses, I used the pronoun which. I could use the pronoun that instead. They are both okay for this kind of sentence, where the relative clause is restrictive.
which sells elephants.
which the shop sold ________ .
In clause (1), which is the subject of the verb sells. In (2), which is the object. It has moved from that gap at the end. We can see that which is behaving like a Noun in these sentences. This is because which is a Noun! It's a special kind of Noun, a Pronoun. Whenever we need to replace a noun inside a relative clause we use which or that - or who if it is a person.
Now let's have a look at a different sentence:
- I play football in the park.
We can divide that sentence into different sections. The Subject is I. The Predicator (the verb) is play and the Object is football. But what about that funny bit at the end, in the park? What's that?
In the park here is an ADJUNCT. Adjuncts like this that get put at the end of sentences usually begin with a Preposition like in, on or at, for example. Adjuncts can also sometimes be Noun Phrases or Adverbs:
- I play football every day.
- I play football daily.
But most often Adjuncts like this begin with a preposition. Adjuncts usually tell us information about why, when, how, who with or where something happened. That kind of thing. This information is always extra information. It isn't part of the essential grammar of the sentence. I play football still makes sense without an adjunct at the end.
The relative word where doesn't usually replace a noun! It replaces an adjunct or a preposition phrase - ones that tell us about where. (Remember that an adjunct will normally include a preposition and a noun). This also means it can't replace the Subject or Direct Object of a verb. It also can't usually replace a noun which is the object of a preposition (although remember that preposition phrases can also be the complements of prepositions). Where nearly always replaces a preposition phrase or an adjunct.
In the original Poster's sentence
- London Bridge is one of the most popular places wwww people want to visit ____.
We can see that that gap at the end there with the missing bit, is the Direct Object of the verb visit. We don't expect to see a preposition after visit either. This word can't be an adjunct or a preposition phrase. It looks like it must be a Noun Phrase. Therefore, we need to use which or that. A good rule-of-thumb test to see if it should be which or where is to see if you could put the word it or them in the gap. If you can, you can use which:
- London Bridge is one of the most popular places which /people want to visit it/.
If you can't but you could put the word there in the gap, then you should use where:
- ... the house where /I used to live there/
Edit note
For some speakers, this rule -that where can't replace direct objects doesn't seem to be so strict. See F.E.'s comment about his variety of English. For my dialect - I'm a British English speaker - this rule is quite strict.
Hope this helps!
Best Answer
Locative Adjuncts
In the sentence above, the Subject is she and the Object is football. What is that bit at the end, in the park? It is a Locative Adjunct (sometimes called a "Locative Adverbial"). It gives us extra information about where something happens.
Usually, Locative Adjuncts are preposition phrases. In the sentence above the Locative Adjunct is a preposition phrase in the park. The Head of the preposition phrase is the preposition in. This preposition has a noun phrase as a Complement. The noun phrase inside the preposition phrase is the park.
The relative words which and where
We use the word where to represent Locative Adjuncts. We use the word which to replace Subjects, Objects or Complements of Prepositions. Adjuncts are usually preposition phrases. Subjects, Objects and preposition Complements are usually noun phrases.
Relative clauses
We often use relative clauses to modify nouns. So we have a main noun, the antecedent, and then we have a relative clause which comes afterwards:
In the sentences above the antecedent is the noun phrase the park, the relative clause is the bit in brackets, [ ]. Let's look at the relative clauses.
These clauses have a wh- word at the beginning. They also have a gap in them:
We understand that the wh- word represents that gap at the end. We can model the grammar like this:
in the park]the park]If we look at the sentences above, we can see that where replaces the whole Locative Adjunct. It replaces the whole preposition phrase, the preposition and the noun.
In contrast, which only replaces the Complement of the preposition. It doesn't replace the preposition itself. We need to keep the preposition in the clause.
We have two choices about what we can do with this preposition that isn't replaced. We can either leave it where it is, or we can move it to the beginning of the relative clause. If we do this it appears in front of it's complement, the word which:
The second sounds quite formal. The first can be used in both formal and informal speech and writing.
The Original Poster's examples
Campus is a countable noun, so we need to use the word a with it. Also, we do indeed study on a campus. However, the antecedent noun, the noun which is being modified, is place, not campus. We study on a campus, but in a place, so we definitely need the preposition in.
In example (1), the writer has kept the preposition in. They have only replaced the Complement of the preposition, a noun phrase. Because of this, they have used the word which. This is correct. We use which to replace noun phrases like this.
In example (2), the writer has used where. This means they should replace the whole Locative Adjunct. They need to delete the whole preposition phrase, not just the noun. So we don't want to see the preposition in here. The sentence should look like this:
We can understand the sentence like this:
in the place].The writer has three options then. They can use any of the following:
Hope this is helpful!
Note:
In case the Original Poster is going to use this sentence, we usually think about a campus as being part of a college or university, we don't use this word very much for schools where there are younger children. We might want to swap the word children for students or young people perhaps.