Manga Ore Dake Haireru Kakushi Dungeon: Kossori Kitaete Sekai Saikyou

Nora is the third son of a noble beggar. He got into a very difficult situation when he lost his job. He did not know what to do, and was already thinking about becoming an adventurer when luck smiled at him.
He heard about a hidden dungeon, which is hidden from prying eyes, where no one knows the passage. According to legend, incredible treasures are stored there: from magical animals to magical tools that will allow you to get unprecedented power in this world. And the guy was opened the entrance to this magical world. All that remained was to keep this place completely secret. However, the world is extremely cruel to the poor aristocrats, so let's see where the story takes the hero.