+1, although I'd extend that to large cities as well. Crowded train stations, stairs, cobblestones, curbs, hotels with no elevators, wet snow or leaves etc. are all a breeze with a backpack. Both your hands are free. And although a backpack may encourage you to pack lighter (which is always a good thing), if you add some packing cubes you'll be surprised how much you can comfortably carry on your back.