Huh! I do this more often than I would care to admit, just where did I park the car?
Now what I have done for a long time is photograph where I have parked, particularly in car parks so I remember what floor and aisle I left the car. The photo also stores the GPS information, of course you might not have a GPS signal in an underground parking garage, but still you have the information right there in the photograph.
But have you noticed in Apple Maps it shows you where you parked your car. If not have a look.
So how does it know where you parked. Well, as I explain in the video below and show you where to find this, it has to do with your iPhone connecting to your car’s bluetooth, a good idea for using hands free phone calls and also listening to your playlists or podcasts. Now, when you park and switch off the car the bluetooth disconnects and this is the prompt that the iPhone uses to mark your location.