The Foot Book (Hardcover), by Theodor Seuss Geisel (Dr. Seuss). The title says it all. In Seuss's wonderful wacky style, this book is all about feet, from start to finish.
"In the house, and on the street, / how many, many feet you meet."
Bookworm's interest at 16 months: He loved it! We read it about five times in a row yesterday (I lost track).
See reviews of other Seuss classics here.
I just looked through the reviews that we haven't posted yet, and I found one more book mildly related to walking, or at least moving. You'll see that the review was written when he was 12 months old, so we're probably due to read this one again after naptime today.
Gallop!: A Scanimation Picture Book (Scanimation Books) (Hardcover), by Rufus Butler Seder. This has a snazzy "motion" effect (which the publishers dub "scanimation") when you turn the pages. I've heard it's a big hit with kids, but I can't say our bookworm has really noticed that yet. Adults all love it, though!
Bookworm's interest at under 12 months: Despite not noticing the motion, he did like this book a lot until he became obsessed with trying to tear open the inserts, and we had to put it away for awhile. We haven't read the sequel yet.