something like "then"

If you see a big park, then you are arrived the place where you want to go. 你看到一個大公園的時候你就到了。= 如果你看到一個大公園你就到了。

In my opinion 就 here has the meaning of "then" and "will". The sentence has the meaning of assumption assuming that you will be there when you see a huge park. I am not a teacher but a native. Hope it helps.

When you see a big park, you are there. 就 在這裡比較接近 已經 already