The Hidden Dungeon Only I Can Enter (Light Novel) Vol. 1

Hidden dungeons--legendary places that no one knows how to enter--are full of extremely rare items, incredibly dangerous beasts, and strange beings that can grant power beyond measure. Noir, the third son of a penniless baronet, just lost his job. He was contemplating becoming an adventurer when fortune struck only a mile from home, and he opened the entrance to just such a dungeon!