Shiki to Ecchi na Kamikakushi

Ordinary sophomore college student Shiki Amano was late to his part-time job. But he had a sudden impulse. He took a shortcut he'd never tried before down a long tunnel, and emerged in a secret garden. R-18 boys love ADV game! 6 characters with thier own routes + 2 bonus scenarios. [Edited from DLsite English]