My favorite relaxation on a Sunday afternoon is to grab a book and relax for a while. I don't get the opportunity to do it as often as I would like, but when I do, I savor the time.
If I have time, I enjoy going to the coast. Santa Cruz, CA has beautiful beaches and nice places to walk along the coast. In summertime is my escapade from the heat of the valley. Looking at the sea makes me relax. Of course I like it when there is no traffic on the route. If it isn't jammed, it will take only 25 minutes drive.
Sunday is used as our Sabbath so we Worship, pray, enjoy each other while doing nothing seriously heavy. We turn our phones off and no TV. Pure family time.