It's 35m deep - for comparison recreational scuba divers go up to 30m deep and professional scuba divers up to 60m deep.
It will have to be well engineered and difficult to repair compared to a land facility, but nothing compared to like the space station.
Very cool idea, after 25 years there should be significant cost savings overall.
If money is imaginary then why can't we guarantee food, shelter, clothing, and education for every single human on this planet.