A million isn't much these days, you should have just said, "if you could buy any one thing" etc...
Anyway, assuming bills are paid, retirement and all that jazz is covered, I'd buy a nice little Victorian that needed some work, and then build in a bunch of secret bookcase staircases and hidden passages behind artwork with peep holes and complete it with a wardrobe appropriate for my future as the old eccentric lady that's always stealing books from the library for no reason.
Nexa
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“It has always been the prerogative of children and half-wits to point out that the emperor has no clothes. But a half-wit remains a half-wit, and the emperor remains an emperor.â€
― Neil Gaiman, The Sandman, Vol. 9: The Kindly Ones