Crystals of Zong is a computer game for the Commodore 64. Crystals of Zong is a simple maze-type action game taking place over a series of levels. Each level consists of nine single-screen rooms arranged in a 3×3 grid. At the centre of each room is a locked treasure area. The treasure areas in the eight edge rooms contain different treasures and the one in the centre room contains a ladder to the next level. The player's task is to navigate the maze-like corridors of the rooms to unlock the treasure areas and get the treasure. After all eight treasures on a level have been taken, the player can descend to the next level via the ladder.
To make the player's job harder, various monsters inhabit the rooms. The monsters start out slow and dim-witted, but become faster and smarter on later levels. Contact with a monster kills the player instantly. In each room, there is a sword, collecting which temporarily gives the player the ability to kill the monsters. After some time, the monsters return.
Source: Wikipedia, "Crystals of Zong," available under the CC-BY-SA License.