For anyone interested in reality:
What’s under the Opera house itself (Reddit link): https://www.reddit.com/r/sydney/comments/djhxyk/underneath_the_opera_house/

The underground carpark for the Opera house that’s actually under the Botanic gardens close by: https://www.abc.net.au/news/2018-02-08/why-is-the-sydney-opera-house-car-park-spiral-in-shape/9270864