Slitherine

OK, how do I make this happen? I have played this game since 2019 and done many campaigns, yet I have never achieved getting a second capital to my knowledge. Clearly it has not been really high priority for me, but I'm in a situation where I want to try it.

It seems to simply be a very rare draw on T3 culture. It's not to be mistaken with the summer palace (which actually prevents the building of the second palace, as it's missing from the pool of my summer palace's region) and I also think I never ran into it for the roughly three years I've been playing. Same thing with the grand palace upgrade in the capital which I've never seen (maybe this time restricted to the most remarkable nations)!