I used the theme generator and got “Journey to the bottom of the sea”.

Well so far, I’ve got just that.

There is a sea, which is sea-like (layered water sprites with sine movement), a bottom to sea and a submarine that journeys there. Also some quite useless fish! It takes just over one minute to get to the bottom.

What’s missing? Actual gameplay.

I’ve yet to decide what the goal is (besides getting to the bottom, obviously) and what obstacles will be presented in achieving said goal.