Bingowings said:

They are meant to be amphibian.

The city looks a bit too posh to be a hideout/bunker.

They don't come off looking amphibian in any way. They look like they would be extremely ill suited to living primarily underwater.......just as we are. We DO go underwater.....but we don't base our civilization there because of our physical limitations.

And who are we to judge the amount of design an alien culture wants to put into a secondary habitat. And if it was where they were doing their cloning they might just put a little more effort into it seeing as they'd be spending large amounts of time there. Naboo isn't Tatooine.....not everything has to be simple and utilitarian.

EDIT: On a side note, go and look at their instruments of war. Things like this should be simple and functional....but their catapults are very decorative and ornate for what they are. Gungans are clearly artistic and take pride in their architecture and the design of everyday objects.