Is there anything to do underwater?
You can get killed by sharks and jelly fish and there is even a treasure map to find ö.ö
And you zoi can collect sea shells and stuff 
(it seems they appear in your inventory after you return to the surface)
If you want to learn more, the video where I took the screenshots from is → here
(The diving content starts at ~ 20:30)
Kjun already mentioned there is more to come for the underwater worlds
Following pics are from the showcase
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