As a part of this effort, today I decided to go for a long walk, with stops here and there for lunch and to buy some minor groceries. I arrived home absolutely exhausted, certain that I had walked some huge distance ... and now Google Maps tells me that I actually walked only 3.6 miles. Wow. I'm even more out of shape than I thought!
Well, this only tells me that doing these kinds of walks is even more important than I realized, because that sort of distance was once trivial, and I want it to be easy for me again. For the past 20 years+, I've considered myself a great and hardy walker, and I plan to get that back.
Edited to Add: Upon further reflection and discussion with Shannon, I realized that my difficulty in today's walk was actually primarily due to how badly my feet were hurting, rather than actual cardiovascular difficulty. I still felt exhausted when I got home, but it was largely due to the fact that the last mile and a half or so of my walk involved pain with every step, which made the walk feel longer and more draining. And for several months now I've been feeling foot pain pretty much every day, sometimes even just walking around the house.
I'm wondering if maybe I've developed plantar fasciitis. A quick search online tells me that it can be brought on by weight gain. More research is needed.