Kallang
It was never "RAF Kallang", Kallang Airport was Singapore's first purposed-built civilian airport whereas RAF Seletar was the first purpose-built airfield/aerodrome in Singapore. Prior to the opening of Seletar, aircraft used the race course for landing and takeoff.
Despite the major changes that have taken place across the whole of Singapore the seaplane ramp at Seletar is still there (although it's in a military facility and therefore off-limits to the public) and can be seen on Google Earth etc.
"By George's" comments in his Post #15 that his old school is now a brewery can be compared to the fact that the old Guardroom at RAF Seletar (now known as Seletar Aerospace Park) is now a kindergarten - oh the irony!