What is Snail Maze? Why, it's a hidden mini-game buried within the Master System's BIOS. To access it, all you have to do is start up the system without a cartridge in it, then press both buttons and Up on the control pad at the same time.
The gameplay's pretty self-explanatory. There are twelve stages and each stage you complete adds some time back onto the timer. Finish all twelve without letting the timer hit zero and you win the game.
Snail Maze is only present in the original model of the Master System. Later versions replaced it with Alex Kidd in Miracle World (Master System II models) or Sonic the Hedgehog (Master System III models, which were only released in Brazil and parts of Europe). Several versions of the original model also have additional games built-in; these include Hang On, Safari Hunt and Missile Defense 3D.