Complex sentence: Many internal refurbishments over years have made it so that three terraced buildings appears as a single complex inside; one can walk from number 11 to number 10, via an internal connecting door, without using the street doors.
Split into simpler sentences: Many internal refurbishments over years have made it so that three terraced buildings appears as a single complex inside. For instance, one can walk from number 11 to number 10, via an internal connecting door, without using the street doors.