Before Tyrion was able to regain his bearing, Tyrion had sensed the other Supernals weird behaviours. It took a while for him to understand the situation.
It turned out that they had never seen a true ocean in their entire life! After the Global Crises, the sea turned out to be one of the most dangerous places in the world.
It was like a gigantic forbidden zone which even a Fiendgod doesn't dare to step into. The monsters at the sea were even more terrifying than those at land and there was even a rumour that several oceans are connected to different worlds but no one who had gone to the ocean to explore or verify had lived to tell the tale.
Several large scale cities close to the sea had all been besieged and destroyed by sea monsters.
Walls more than a thousand feet tall couldn't hold these sea monsters. Apart from their massive numbers, their immense size and strength could easily wipe out any city.