It has been de rigeur in Greece to take your shoes off when entering a house, as owner or guest. Indeed, Greek has borrowed the Turkish proverbial expression about it: to “hand someone their shoes” is to invite them to get the hell out of your house. (του ’δωσα τα παπούτσια στο χέρι/pabuçu eline vermek).
I will note that while it’s a norm I follow to this day as a householder, it’s not one I experienced as a guest in Greece: I don’t remember ever having to remove my shoes when a guest. In fact, it was only when I crashed at an uncle’s place for a few days that the spare slippers would surface.