Retired means I'm not looking to relax. I book okay-not-great hotels based on proximity to public transportation and plan to spend as little time in them as possible. I like longer trips -- 3-6 weeks -- and break them up between cities and countryside. We live in an area where mountain hikes are a dime a dozen so I don't look for that when traveling but enjoy if it happens to be there.
I'm not a fan of groups but it is nice to break up long, DIY trips with a cruise or something just to have a week or two where someone else is worrying about the details. By the end, I'm usually close to wanting to throw myself off the bow and happy to be on our own again, refreshed and ready to go.
Historical sites, museums, walking tours, food tours, leisurely lunches and dinners (preferably outdoors) with lots and lots of walking during the day and into the evening. Jogging in the park or along the river if my feet are up to it. I try to get a walking tour and a city museum in early so as to have at some context for what we'll be seeing. We typically average 8 miles of walking a day, some days as much as 12. This is because we enjoy exploring all the nooks and crannies and off-the-beaten-trail parts and because we need to walk off all those leisurely lunches and dinners.
We're enjoying driving less and less these days, which makes touring the smaller villages difficult. There are still plenty of smaller cities and towns we haven't been to that are accessible by train, but at some point we'll rent a car again and hope we don't get run off a cliff in southern France or sideswipe a limestone wall on a one-car-wide road with 2-way traffic in the Cotswolds.