Sanctuary

This world is called Sanctuary by its intelligent inhabitants. It orbits a star not too much unlike our own, although it is hotter.
There is one large continent, the rest of the planet is covered in water. Atmospheric conditions are conducive to frequent, severe storms, forcing creatures on land to seek shelter often.
Luckily for them, there are large natural cave systems, which they have expanded over time.
Eventually, the majority of life simply adapted to life entirely underground.
Most creatures have methods of perception aside from sight, such as sonar. Underground rivers are common, and metals are plentiful.
More details may follow, and some things may be changed in the future. If you find any unaddressed conflicts in data between posts, assume the most recent is correct.