The first commercial flight from Heathrow was on 1 January 1946, now (just over) 75 years ago. This was by British South American Airways (later re-incorporated into BOAC) of a converted Lancaster to Buenos Aires.
It would be nine years or so before there was anything resembling a real terminal building. At first there were only a series of former army marquees strung along the Bath Road, unheated and containing little more than chairs, settees and small tables. Your flight was allocated to one of these and you walked directly to the plane from there across wooden duckboards when it was ready to go. Later these tents were augmented by semi-permanent wooden huts and this was referred to as "Northside" as the central area was gradually developed and this ramshackle arrangement didn't close to the general public until 1961 with the opening of the second central terminal, Oceanic (now Terminal 3).
Other oddity was that through the 1960s and early 1970s Heathrow was a tourist destination in its own right with the terrace gardens on top of the Queen's Building and Europa Terminal to view the runway operations.
Heathrow - the airport under construction for 75+ years that could be completed in another 30. Maybe.