The veterans here at CivFanatics will remember Civ2 and Civ3: Civ2 had a throne room, which you could upgrade and make more fancy whenever your had a we-love-the-X day in one of your cities. Civ3 did something similar with a palace. Both features were nice to look at, but did not affect the gameplay at all, and were therefore probably not included in later iterations. They were very beloved though. PCGamesN has an article today here, that there is a Civ6 mod which brings both of them back to Civ6.
So if you want to have the glorious days of palace and throne room building back, you can have them now ;).
You can find the mod here: https://forums.civfanatics.com/threads/technoluddites-mods.673401/ , made by our veteran member Technoluddite.