Tengai Makyou: Fuun Kabuki Den

Save your game before beating the last boss. After the all the scenes and credits are over, you'll come to a screen with a big white Japanese character and a curtain in the background. In this screen, press I and you'll hear a sound. Now, reset the game and load your save file. Go to the north-east corner of the room with the 3 treasure chests and, if done right, you'll fall through a secret hole into the Dharma Cat Hall where you'll have access to all the music, cinemas, minigames and more.