俺だけ入れる隠しダンジョン～こっそり鍛えて世界最強～

The Hidden Dungeon Only I Can Enter, Special training in the Secret Dungeon, 俺だけ入れる隠しダンジョン～こっそり鍛えて世界最強～, Ore Dake Haireru Kakushi Dungeon: Kossori Kitaete Sekai Saikyou

誰も入る方法を知らない伝説の場所である隠しダンジョンには、非常に珍しいアイテム、信じられないほど危険な獣、そして計り知れない力を与える奇妙な存在がいっぱいです。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!