Milon's Secret Castle (迷宮組曲; Meikyū Kumikyoku, literally "The Maze Suite") is an action-adventure game released by Hudson Soft for the Nintendo Famicom (Japan) on November 13, 1986, the Nintendo Entertainment System (USA) in September, 1988, and the Game Boy (in Japan: ミロンの迷宮組曲; Miron no Meikyū Kumikyoku, or "Milon's Maze Suite") on March 26, 1993.
The game has generally been considered extremely difficult and frustrating. There are no save points, and once a player runs out of life, the game is over, however, it is possible to continue after obtaining the first crystal. Unlike in most platform games of the era, Milon doesn't "blink" to become briefly invincible when he is attacked by an enemy, which means his energy can be sapped very quickly if he doesn't move away.
Each room of the castle contains secrets similar to those of the Super Mario Bros. series; the secrets are uncovered by shooting bubbles into invisible trigger objects.
An interesting cumulative side-quest involves finding music boxes. By touching a music box, Milon is transported to a mini-game where he attempts to pick up many musical notes as possible, with extra points given for sharps and negative points given for accidentally picking up flats. The first time the player reaches the mini-game, only one elf with a drum appears to play the music. Each time the player collects a music box and is transported to the mini-game, a new elf with a new instrument appears, and the song gets more interesting.
The Game Boy version of the game does include a password feature (otherwise it is mostly identical to the NES game).
Milon also makes a cameo appearance in Saturn Bomberman. There are hidden Milon tiles in Star Soldier that can only be uncovered and destroyed for a 40,000 point bonus when certain score conditions are met.