Do you think the sentence above grammatically right? As far as I know, the noun “south” needs an definite article: the. Is “south” in the sentence an adjective? Then, how about “Which way is the south?” Can I speak that way?
“Which way is south?” is a typical question, and it is also a grammatically correct way to ask about a very general compass direction.
Adding the word “the” to that question would not be natural. It would sound as though you were asking about a specific location rather than a general compass direction.
You can use “the” for more specific locations/regions and with prepositions, for example:
‘South’ without an article is essentially direction and with the article invariably indicates location. You might be interested to know that ‘south’ with its sense of direction can also be used in financial expressions of particular interest to many economies at the moment. We talk about the market going south, suggesting that the market is going down or dropping.