The mega mall was built on the former site of the Funabashi Health Center, which was located in Funabashi City, an eastern Tokyo suburb. The amusement park opened in late 1955 and was in operation until mid-1977. 
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LALAPORT FUNABASHI CENTER (TOKYO-BAY) was the initial Lalaport-branded mall and the first retail facility built by Mitsui. Revolutionary in design, the facility brought the great outdoors indoors by use of landscaping and natural lighting. It was also one of -if not- the world's first environmentally-friendly shopping and entertainment complexes.
Photo from Wikipedia / "Mayuno"