I retired 10 months ago and yes I had a plan. I've always had interests outside work (cycling, running, camping, sailing, fishing, rc flying travelling.........etc). The first 6 months of retirement were exhausting - I spend the mornings doing work around the house (I live on a few acres - so they need tending). After lunch, I enjoy my hobbies and by the evening I'm so tired that I go to bed EARLIER than when I used to work.
I thought the winters would be boring (Im in NJ) but I have indoor projects which keep me busy and I reserve rainy days for museums, library, shows...
I have a "list" of activities in case which I keep with things that I want to do and as I travel locally I keep a note of other activities in the area.
So far been quite busy but I do know that there are people who retire and sit in a chair all day and are happy - each to his how