​Plate with inverted “T” shape opening, set into the wall behind the desk in my hotel suite in France – the text underneath says “lagrand.”

Euro coin for scale! There are plug points in the wall further along, but a good meter away. It almost looks like the sort of thing that you slide a security chain into – but it’s nowhere near the door or windows. Looking into thr opening side on (pic 3) I can see some metal “teeth” or something.

I am British and travel fairly extensively, particularly on the continent, but I don’t think I’ve ever seen one of these before.