At some point I realized that there was no reason I had to wait until retirement to realize this fantasy, and now many of my Saturdays begin with a walk to a local park, followed by several hours of reading. It's just as pleasurable as I had expected, and it's actually been surprisingly easy to make this happen now that I've made it a priority. It doesn't even take a whole day; there are plenty of Saturdays when I go out to read during the morning and still have the rest of the day free for whatever chores or social engagements are vying for my attention. I even find myself doing it on weekday afternoons evenings, especially in summer when the days are long.
Another thing that has led to me reading more books is just giving myself permission to read books in increments of 15 minutes or less during random moments of downtime. Moments on/waiting for the tram or between phone meetings that I would have spent checking Twitter on my phone can just as easily be spent reading a book. This isn't so good for certain kinds of content that you might want to devote more attention to, but I've found that I'm perfectly capable of enjoying fiction in 10-minute increments without significantly diminishing my enjoyment of it. And oftentimes, reading bits of a novel throughout the day often gives me a certain amount of momentum that makes me want to continue reading the book during my free time in the evening during time that I might have otherwise spent watching TV, browsing reddit/facebook, etc.