Titan Crater was formed when a massive asteroid smashed into the Tetras seabed. It had dramatic effects on the land, but scarred the sea floor as well.
The basin of the crater is wide and flat in the centre, but slopes up first very gently and then very steeply when you get to the walls of the crater. These rise higher than the rest of the seabed. The basin isn't smooth, but instead pockmarked, and rocks lay all over the place.
Titan Crater was, of course, non existent before the asteroid impact. Afterwards, sea creatures started to use the massive basin as a home, because it gave them an open space to swim around in, as well as lots of hiding places from predators.