Gordon and Susan's apartment is the first floor apartment in the brownstone of 123 Sesame Street. The apartment was used as a hangout spot in the early Sesame Street episodes, particularly the kitchen and dining room area. According to Episode 3507, their apartment is number 1F.
In Episode 2689, the apartment gets damaged in a fire started in the building's basement. Big Bird stayed there for two days while his nest was being rebuilt after a hurricane destroyed it. (Episodes 3976-3980.)