Dinorwig power station [0] is in the middle of a national park. A pretty one, even.

[0] https://en.wikipedia.org/wiki/Dinorwig_Power_Station

Yes, and add you can see it's already been developed - for over 60 years. That's not to say more can't be developed, but the rate of new development has been pretty low, and the prevailing belief was that this was the result of all of the best resources being used up.

...and even then they built it mostly inside the mountain, next to an old slate quarry. Which is going to help national park acceptability but not the unit cost of construction I suspect.

Doesn't need to be near population center. The majority of the energy I've used in my life comes from a dam over a thousand kilometres from where I live.

https://en.wikipedia.org/wiki/James_Bay_Project