Why use "which" instead of "where" here?

"Where" is already implicit in "the Great Wall." Which is used because the Great Wall is a thing.

This is the last question by you that i will answer. I'm not going to kibitz your instructor's examinations. Do you expect to take the responses to your instructor saying: "See, this native speaker says you're wrong"? You've got two strikes against you already.

Here's when "where" would be used:

The Great Wall is the place where visiting Chinese like to take pictures.

Functional is 'place' - position/location - Where.
Functional is 'object' - item/thing - Which.

I would use 'that'. Because it covers both parallels

God people are dense. Do you people actually read and make an effort to understand the OP? That was a question on a test, for which he was marked down. Rewriting the sentence is completely irrelevant to his question.

His 'only' question was 'Why is this (That he referenced) so?'
I granted him the answer to 'why'... then my preferred usage thereof.

It's not us 'dense' people who have to endure your bitterness, Setanta, It's all for you to bear and those you, ignorantly (not an insult - naive-ignorance) extend it unto.

If you think about the physicality of the Great Wall of China it extends for many miles - hence, its locality is over a broad area in China.

The Great Wall could be visited in several localities...so the proper (or logical) way of referring to it would by 'which' (meaning it's a thing...not found in one specific place)...an edifice that has many locations.

Dear Setanta. You have it backwards. I AM a native instructor who is trying to decipher these esoteric local exam questions for my students. Two frustrating things that happen during esl instruction:
1. I know this is wrong but I can't explain it.
2. I have no idea why this is so and I am a native speaker.

Thank you everyone! It's been most helpful.

Just Google "use of where and which in clauses" and lots of theories come up, including that "which" is the more formal usage, "where" the informal.

No, it's not wrong. As is the case with the sentence in your other thread, one might allege that it is awkward (i don't agree about this particular sentence--the other one is absurd). However, neither this sentence nor the other sentence is either illogical or incorrect.

One of our members here who improved his English a great deal while here posted a series of sentences over time, last year, and they were truly awful. They were not just awkward, they were wrong. These are not wrong, but i can see why you would find them jarring to your ear.

Finally, don't call me "dear." We don't know one another, so i am obviously not dear to you. I abhor false bonhomie and what seems to be a Chinese penchant for trying to make online posts into friendly letters--they are not. Maybe you've been over there a little too long.

I agree - but the question (in and of itself) in no way, at all, grants (unless original question stressed 'functional' by 'text-embellishment', visually, we are unaware of) us a route to what is functional.
It tells us that 'The Great Wall IS a PLACE. That's IT!
The very question is TELLING us What the "Great Wall" is - It is a PLACE! - Therefor "Where" applies.
ps, I'm not 'shouting'. I just apply upper-case to emphasise.

If the (in and of itself) question read "Great Wall is structure" (object) - "Which" applies.

"That" bypasses the ambiguity-factor.

tomato , tomahto

However, what the OP asked here is a choice of which or where.

Your point being?
I must, by some standardised rule - Respond in only the fashion/style, befitting your approval?

I'm happy with my response.

... and your response doesn't answer what OP asked.

Have a nice day.

Yes it does - You just view it otherwise.

Does not, does not...sticking tongue out and stamping my feet!

Cheers, Rag! Made me smile.