All very good advice. Walking boots for rough terrain, comfortable trainers for decent tracks and footpaths. Even walking about an old city or town may present problems, like slippery cobbles or stone setts, if you don't have a good tread on your shoes (I found that out in Portugal with comfortable shoes but no tread, great on desert surfaces but not recommended on cobbles!). I too would not recommend sandals for even the shortest walk, as they are usually a loose fit and may cause severe rubbing of the feet.