Mentioned in the game, but never really expanded on in any depth, was the concept of the
Sea City.

We really don't know what they look like, but a quick Google will provide you with a plethora of images. Some practical, and others... well...

Not so much.
I prefer thinking of them as surface cities, with the Cetaceans handling the underwater portions.
And they would vary from seasteading structures like this:

To floating designs like this:

So have you ever had your PCs visit one? What was it like?