There are a few smells that are absolute and can take you back to a time/place/memory with one whiff.

The smell of my wife's perfume always makes me smile, always
JP5 jet fuel puts me back in the Indian Ocean on the flight deck of an aircraft carrier
Coppertone sun tan lotion transports me to the years living near the ocean

These lilacs? Immediately takes me back to growing up as we had this massive lilac tree in our yard that made the entire home smell like lilacs for a few weeks every spring...