I am not useless

In a certain world 50 years before "gorlood incident" happened. numerous portal suddenly pop out of thin air. The portal is called "dungeon" by the human population that live in that world. you all can already guess what it's inside the dungeon, yes.. it has monster and trasure box inside the dungeon i welcome feedback. i'm still new at writing novel if readers find any wrong grammar readers may feedback/give advice for me to fix the grammar.