Here’s an interesting concept… Let us explore.
How might it work – for power, food, basic industry?
Is there a class structure for the residents (what is considered “better accommodations” – closer to the water, or higher up)?
Is it (somehow) stationary or does it float freely?
Does it have some kind of propulsion system?
Is this a structure developed by an indigenous population, or settlers from elsewhere?
What prompted the construction (vacation destination, colonization, penal colony, survival from global warming, accommodate population explosion, quarantine facility – or sanctuary)?
What kind of people live there – humans? Aquatic-hybrids? Visitors (non-aquatic species – like an embassy of sorts)?
What happens when significant weather happens – hurricane, monsoon, tidal waves? Or larger things in the ocean than them?
What about when there start to be mechanical failures?
Is there a routine for cleaning the underwater surfaces, or do they let things grow?
Are there other similar structures? Is it possible to travel between them?
Then what happens…?