Hidden Depths describes itself as a "third person, non-combat, relaxploration adventure", which is an apt description.
Miku and her younger brother Taku are exploring a watery city, one in which a large black plant-like mass has taken hold,
one which “swallows life and spits out copies.”

They are alone, except for strange manifestations of the previous inhabitants which ‘populate’ the inundated buildings,
and an array of animals and sea creatures.

Find out more in flotsam's review of

******** Submerged: Hidden Depths ********