Willy continues through the next cavern and explores new things including a mysterious message...

Miner Willy gets trapped in an unexpected place, in a system of hidden caverns, possessed probably by some ancient miners, asked by a strange man to follow him, Willy starts his journey

Yup. It's fanfic for a game that's nearly as old as I am. Manic Miner didn't have a plot, so I feel, as one of the people who played it obsessively, as though I owe it one.