Okay, here's my suggestion. Coming straight of the end of the arch walkway, where the sky begins, should be a pathway. It must slowly become narrower and narrower until it fades completely. Surrounding the pathway should be grass/flowers, whatever you want around it.
If you'd like, I can draw some sketchy looking lines to demonstraight how you could put a pathway. But if you don't want a pathway, you need some sort of grass or landscaped feature fading, which can be done using a gradient. Using something other than a solid color is key.
I hope that made sense.
But since I can be bad at explaining things, it probably doesn't.