I have a very distinct memory of disembarking from the Budapest to Belgrade night train to the smells of leaded fuel in Belgrade.
Budapest was no standard of cleanliness at the time (late 90s), however Belgrade was truly still in its post-war phase and had all of the energy, anger and edge of a place that had been pretty beaten up.
We were robbed, given a pistol in a nightclub (still have no idea what was going on there, I just remember being really surprised that pistols came in styrofoam and shrink-wrap packages when they are new... Being from Canada I had never even seen a pistol before), were surrounded by really beautiful people who we thought wanted something from us but who were only generous and kind, and .... the smell.
The smell of that leaded fuel was everywhere. It smelled sweet and was so unique. It's what has stuck with me 20+ years later.
One other side note from that trip. We were in the countryside (mean to be meeting a friend from home in his ancestral/family village but took the wrong bus) and someone in the village directed us in to a pub that was basically an old barn. Inside there were many middle eastern guys and a mix of Serbian and english speaking people. I was given a pin by one of the middle eastern guys after I threw an excellent game of darts on the dartboard next to him.
Years later I had a job for a defense contractor and the subject of that trip and the pin came up. I showed him a picture of it and he recognized it instantly: al-Aqsa Martyrs' Brigades. I looked it up and so it was.
We were put up with a local elderly woman who served us some type of soup in the morning and then someone gave us a ride out of town to a bus stop that had service that day. We waited only an hour until the first car came along, reeking of leaded fuel.