If you are given 100 Million US Dollar on a condition that you can only buy a house with that money and that too in your favorite locality of the world. Where would that be?
Nationality, Citizenship,etc are no problem. No property tax either. You need to choose your favorite neighborhood in your most favorite country/city of the world.
I personally would choose a giant Palazzo/Bungalow/Mansion in Mellieha, Malta.