Your experience of a city is at least always partially ruled by the weather, which is why I make a case that you need to experience a city in a beautiful sunset or sunrise - ideally up high - before proclaiming it beautiful or not. It was golden sunset every day of the blessed five days we spent in Paris, including the last day where we caught the Arc de Triomphe illuminated by the sunset and the streetlights glowing like stars at the Place de la Concorde.
Our first afternoon in Paris - featuring unprecedented levels of warmth and greenery compared to still-bare-branched Denmark - was most irreplaceable. The word 'beautiful' feels lacking - what I remember was the golden light illuminating the mass of complex ironwork of the Eiffel Tower as we climbed the stairs (tiring but recommended), casting shadows over the blue-roofed arrondissement jungle below, turning blood-red as we reached the peak.
I'll forever remember walking towards the Pont de Bir-Hakeim (the Inception bridge!) as the last of the sunset was illuminating the windows of the building opposite the Seine, and turning around to see the moment the lights began sparkling on the Eiffel Tower, just struck with 'oh my god, I'm in Paris.'
City of Light, but not quite in the way you might expect.