There is fun for all ages on a Sunday!
Take a boat out for the day.
Most of us folks have a body of water near our home and a lot of us have a canoe, rowboat, small sailboat, power boat or a kayak.
Sunday is a marvellous day to take one out for the afternoon. The fun of going out in a boat is that you don't get to do it every day and, so it is special.
Bring a fishing pole and some bait or lures and maybe catch a fish or two or three.
It is a fun time for a beer on the shore afterward (if you are old enough) and can make for a nice exercise as well as a great way to get the troubles of the week off of your mind for a while.
Oh and it can be super romantic.