Terminal 3 Roof
The Oceanic Terminal (now T3) opened in 1961 replacing the "temporary" facilities used by long haul aircraft at Heathrow North Terminal (previously London Airport North).
At the time Queens Building was the European terminal and included a small domestic arrivals/departure area and many of the airport's offices. Above all of this was the Spectators' area which included the terraces, cafeteria and restaurant, an enthusiasts' shop and an exhibit area. Summer weekends and many summer weekdays offered a running commentary on the movements.
Entry was, if I remember 6d (2.5p) for under 16s, 1/- (5p) for adults.
The area gave excellent views over the Queens Building ramp, the approaches from the east to the parallel runways and of runway 23, not to mention views of the BEA, BOAC and Eagle hangars.
Before the Oceanic Terminal was opened the North Terminal movements could also be monitored but once the new terminal opened, a number of aircraft arrived before the Queens Building spectator area opened each day and departed after closure.
Those "in the know" would, when Queens Building closed, make their way to the Oceanic Terminal and onto the small spectator gallery on the roof which was free entry.
I was first told of this on a visit in 1962 (I lived in the Manchester area) and when I was regularly working in London in 1965/1966 I would drive out to the Oceanic Terminal on summer evenings and make my way onto the roof.
Whilst the spot was useless for observing anything on the Queens Building ramp or aircraft landing short in a westerly direction, westerly take offs could be observed plus, of course, the exotica on the ramp below.
The terminal was first modified in 1966/67 and the gallery remained for a short while but was closed sometime in 1967 as the roofspace was taken over with extra heating and ventilation equipment.