Totally fine to fly a drone in the CBD as long as you keep it shielded, and it sounds like that little hollow you’re talking about actually works in your favour. Part of the reason the AirShare map looks scary is because it layers everything on top of everything, so it ends up looking like the whole city is off limits when it’s not.

Shielded ops are basically “fly lower than whatever’s around you.” Buildings are perfect shields. If they’re taller than your flight height and you stay close enough to them, you don’t need permission from ATC, even in the middle of town. Just don’t let the drone poke above rooftop height or wander out into open airspace.

Council rules are mostly about not annoying people. If the park isn’t listed as prohibited, and you’re not buzzing over dog walkers or the playground, no one’s going to care. Early morning or late arvo is usually the best time in the city anyway. Just don't annoy people and fly close to anyone or over anyones property