I do not know if every September is open, but the entrance is not free, it costs $ 40.00 USD, I buy the city pass online, and it is cheaper, it costs $ 108 usd and you have the right to choose 5 visits out of 7 Aquarius, Science Museum, planetarium, skydeck building, 360 Deck building, art museum and another museum that I don't remember the name. I hope the information is usefull. Good luck.
They will provide the tickets when you go there at the tickets counter along with passes for dophin show as they are at particular times only
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