I visited Notre Dame in July 2018, just a day or two after my visit to Sacré-Cœur. I have to say I was disappointed. After the paleness and warmth that greeted me at Sacré-Cœur, Notre Dame felt a bit grubby: too grey, too tall, too dark, and too businesslike. In truth, Notre Dame is every bit as clean as Sacré-Cœur; I just didn’t respond to it in the same way. Maybe it was the number of people inside, maybe it was the long snaking queue to get in, maybe it was the wrong end of a hot and tiring day.
This catholic cathedral dedicated to Our Lady was famously the home of the fictional “Hunchback”, and there is lots of interesting information about the church on its Wikipedia page https://en.m.wikipedia.org/wiki/Notre-Dame_de_Paris. The queues were too long and the day too hot to climb the towers, but I’m sure the view would have been amazing.