My S.O. and I would do some traveling, mainly in the U.S. There's so much to see here. We might try to do a "Ballpark/Theme Park" road trip. We did this a couple years ago...started at Kennywood Park just outside of Pittsburgh, then caught a Pirates game the next night.
--Drove up to Erie the next morning...Waldameer Park and Splash Lagoon.
--Next day, on to Cleveland to catch the Tribe, next day was Cedar Point, and finally a couple of days in Cincy for Kings Island and a game at Great American Ballpark.
Maybe we'd try to take a shot at getting to all 30 MLB parks and a bunch of theme parks.
More mundanely, we'd get a lot of golfing in, a lot of afternoons at Wheeling Island Greyhound Track, a lot of bike riding. Maybe we'd try to do Pittsburgh to Washington along the Great Allegheny Passage and (I think) C & O Canal Trail.
I know one thing....we would not have a boring retirement.