If you’ve only got one day in Croatia, I’d pick one city and enjoy it properly. Dubrovnik or Split are great choices. In Dubrovnik, walk the old city walls early (less crowded), explore the Old Town streets, and maybe relax by the sea in the afternoon. In Split, check out Diocletian’s Palace, wander the old town, then head to the Riva promenade or a nearby beach. I’d personally avoid overplanning, just soak in the vibe, grab some local food, and enjoy the scenery.