<p>Wow. This is tough, even for a grammar nazi like me. </p>
<p>I am not 100%, but I believe it is A. </p>
<p>“On a trip…big city” is a prepositional phrase. Thus, a comma is required. Additionally, “New York” is nonessential information, which means it also requires the comma.</p>
<p>A is the most right, I think, but it’s an awkward sentence. You don’t want to end a sentence with a little phrase like that. If I were writing this in an essay, I’d probably write something more like: “Here I was, in New York! The Big Apple itself!”</p>