Like many here, I've seen many 'off-airfield' aircraft here and there over the years, but tbh I can't remember too many of them in detail. Taking a photo, or sharing the experience with regular friends helps bed the memory in somehow! Many of mine were pre-smartphone days and usually in an unexpected/spontaneous way.
I do recall various aircraft, or sections thereof located in AirCadet or Scout properties around the UK, usually spotted from a train window, or top deck of a bus.