Milon's Secret Castle is an adventure puzzle platformer game for the Nintendo Entertainment System (NES) developed by Hudson Soft. The game features Milon, a boy from the peaceful country of Hudson, who embarks on a perilous journey to rescue Queen Eliza from an evil warlord. Players navigate through a large and mysterious multilevel castle filled with hidden doors and secret rooms. Various power-ups, such as bubbles and music notes, can be used as weaponry or for solving puzzles. The gameplay revolves around exploration and the completion of diverse tasks in order to progress.