Assuming we're talking about having enough money to retire with a decent income, I would enroll in an online art history degree course from an institution like

Assuming we're talking about having enough money to retire with a decent income, I would enroll in an online art history degree course from an institution like the Open University in the UK. Then I'd spend my time traveling around the world looking at the paintings and visiting historical locations while I learn. I'd live in Florence for a few months while learning about the history of Renaissance art and so on.