The Sunflower Fields appear in Lucas's dream during Chapter 6. This is a minor area, and the only time you see Hinawa after she dies. It is a straight-forward place, but it is found in the skies. Now, the Mother series is strange, but this symbolizes it is a dream, and could never truly happen.
As mentioned early, this spot only appears in Mother 3. It is very short. You just go left and right, then you'll start the next chapter after a few events. There is no speaking here other than Boney barking at Lucas.
There are no enemies in the Sunflower Fields. That makes it an easy area to navigate in.