You start by going to your favorite park for the day have a nice romantic dinner and ending it with a cocktail and your favorite fireworks show and then you look into your fiancés eyes (mid fireworks) (hold hands) and say wouldn't it be amazing to get married here (bat your lashes and smile). Worked for me, even though we ended up choosing cruise over world it still worked. By the way I chose the cruise because while I was throwing around the idea with my sisters I saw how excited they got about going on a cruise and I knew it would be fun.
Just a suggestion please feel free to modify the above with your own words and what feels natural

Congrats!!! Start your planning wherever you choose to get married.