imagine an urban exploration game...
an empty city, abandoned because the sea rose to claim it. concrete skeletons half submerged. crows roosting in the high rise offices.
the player, the explorer, as a semiaquatic creature able to climb and dive
@chr it's not exactly that (no diving) but you might be interested in 'submerged' https://www.youtube.com/watch?v=mi8sXnrHa64