but it's so true, I just got back from Paris and my walking shoes were a lifesaver. Because they did what good shoes are supposed to do, and so I never had to think about them and my feet/knees/hips never ached. I didn't really realize until the trip was almost over just how nice it is to not have to worry about feet!
For the record, these were ASICS all-black walking shoes that I picked up at an ASICS outlet store, on sale. Meaning they cost virtually nothing, but they were priceless! I'm not necessarily recommending this brand since shoes are so personal, but please make sure you don't go on a trip without two pairs of broken-in, comfortable walking shoes. And waterproof if applicable. My wife had nothing but trouble with the shoes she brought and she was in pain the whole time (we had to make a mercy run to Galeries Lafayette and Printemps so she could try and find something).