Wonders!
Greetings!
I think any large city should have a rich history. An off-shoot of that line of thought, is that there should be a great Wonder or two. A great landmark. Imagine a huge tower of glowing crystal that is enchanted with music, for example. Perhaps it has a great enclosed waterfall, that is lit up at night. This might be some greta thing, a hundred or more feet high, and sixty-hundred feet or more wide. Imagine the spectacle!
Perhaps a great arena, or Collosium. Imagine a huge enclosed park of incredible trees, and beautiful lakes.
A vast fortress, and perhaps a war-memorial. A great tower, or a great lighthouse. Imagine a vast theater, partially above ground, and partially tunneled out into the sea with hallways of crystal and polished coral, all with breathtaking views of the sea from underwater. Imagine this vast building having unique auditory effects, and a magnificent amphitheater. It would be an entertainment mecca for the entire region! It could have famous troupes of gorgeous dancing girls, and a guild of renowned thespians; There could be several of the greatest singers and musicians that work there. And so on.
Think about brothels, gambling casinos, labor guilds, as well as governmental offices. Royal Agricultural Center, or the Royal Maritime Guild, or the Royal Museum of Sea Creatures. (or Zoo)
Ancient Rome had a number of similar things, so there is nothing preventing you from even a *realistic* standpoint of being really diverse with what your large coastal city can offer!
Semper Fidelis,
SHARK