I remember reading somewhere on one of the URA planning documentations (somewhere in the bowels of the NUS Central Library) that the original location for this station was to be at Changi Airport. There were two alignments that were studied, one above ground and one underground. The above ground alignment would have culminated in the Foster designed station, serving as an architectural icon at the center of the airport complex. However, it was decided that the vista of the Changi control tower was too iconic to be blocked by this new MRT station, and hence the underground alignment was chosen. The Foster design was also too good to be discarded, and hence it was moved to the Expo station instead.