Smell is unique among the senses in that it will often trigger vivid

Smell often trigger vivid memory. This is because of the anatomy of the olfactory pathway. The nasal mucosa senses odorant molecules wherein the olfactory nerve will transduce the signal to the olfactory bulb to the olfactory cortex, bypassing the thalamus (unlike other senses) Anatomically and physiologically, the olfactory cortex is closely related to the amygdala which is associated with memory formation.

Primary example is that a certain smell of a perfume of your ex-lover can trigger vivid memories even if it was many years ago.