For me, it is Rome, Italy. I visited Rome last year for a week and absolutely fell in love with everything the city had to offer!
The entire city is practically a museum; every brick tells a different story! I spent most of my time exploring the historic monuments and museums, but I still feel that 7 days were NOT enough to experience everything in entirety.
Apart from the historic significance of the city, I just loved how friendly the people were. The energetic vibe of the city is very intoxicating.
Another BIG plus was the amazing Italian food (of course). I had the best Spaghetti Carbonara of my life there and definitely the best Gelato ever! Gained about 2 kgs in one week because of the 5 meals a day routine, but it was absolutely worth it.
And lastly, I became absolutely obsessed with the Trevi fountain. In my opinion, it is one of the most beautiful pieces of art I've witnessed till date. And I spent quite a lot of time just admiring its beauty, but still couldn't do justice to what it actually deserved.

So what is one city that you fell in love with after you visited it, and why?
Would love to hear your experiences!