Anyone know where this plug goes?

Not very familiar with the Europe spec, but my guess would be the headlight leveling motor. Check for a similarly-shaped connector emerging from behind the headlight assembly.

 

Whatever it is, it seems to be capped off with rubber plugs and not male or female terminals. I doubt that it plugs into anything. Probably used for some feature that your trim didn't come with from the factory.

Posted via the PriusChat mobile app.

 

I checked and could not find anything like that (plugged or not) in our Prius. It is LHD. That loose cable end is rather long for Japanese works by the way. They usually pack and wrap things nice and tidy. Perhaps zip tie had been cut during some maintenance and got never tied again(?). Just tie it up and carry on