Some say that olfaction is the sense most closely associated with memory, and two experiences I've had in the past year or so give some credence to that notion. The first experience happened many months ago when I came down with a bad cold. I don't get seriously sick very often, so the last time I'd suffered from a similar malady was just before and during the first few days of my study abroad in Germany my freshman year of college. It sounds paradoxical, but the smells associated with having my nose completely stopped up again caused vivid memories of Wittenberg, specifically of the house I lived in, to flash in mind for the duration of the cold.
The second experience is still ongoing. As I walk around Cologne, a city 400 kilometers from Wittenberg, I nonetheless notice a common odor that causes me to remember little things about my experiences three years ago I had long since forgotten. As I've traveled throughout many countries between then and now, it seems that this smell is indeed peculiar to Germany. It's odd because I didn't notice the smell before--I had to return for it to stick out it my mind. This is completely unlike an experience I had many years ago in Edinburgh, where the smell of the city was immediately noticeable and I was sure I'd never forget it.
Perhaps one reason olfaction has such a powerful link to memory is because smells are the hardest to capture and thus unusually distinctive. One can take pictures and videos to remind one of the sights, make a recording or listen to specific music for sounds, take along some object or souvenir for touch, bring along or cook a dish for the taste, but how does one capture a scent? Some would come naturally with the other senses, such as when one cooks a particular dish, but there doesn't seem to be a good way to capture the street scents of a city, so to speak. Thus, unlike with sight or sound, one can only experience smell under specific and rare conditions, and when finally exposed to it, the effects are powerful.
At least for now, I have a Cologne not packaged in any bottle to serve as my olfactory reminder.