walk-in

person who walks in without having an appointment; "the emergency room was overrun with walk-ins"

an operative who initiates his own defection (usually to a hostile country) for political asylum

an assured victory (especially in an election)

a small room large enough to admit entrance

(of e.g. closets or refrigerators) extending very far enough back to allow a person to enter; "a deep walk-in refrigerator"; "walk-in closets"