The Hidden Dungeon Only I Can Enter

Noir, third son of a “beggar noble,” lost his job and was at a loss, but fortune struck just as he was contemplating becoming an adventurer. Hidden Dungeons that no one knows how to enter. Legendary places full of extremely rare magical beasts, magic tools for power beyond measure and items that would be considered a rarity all over the world. To such a dungeon the entrance was opened. “Without telling anyone about this place I’ll secretly become the strongest.” This world is harsh to nobles of poverty. Without authority or honor, if I could at least acquire power―― — Description from novelcodex.org