Crystal Castles is a 3D Pacman variant, where the aim of the game is to guide Bentley Bear around and clear up all the gems to advance to the next screen. The game screens are built on platforms with elevators joining the upper and lower levels and there are tunnels through which you can traverse the screen. All the while you are pursued by Gem Eaters which suck up the gems around the maze, and indestructible trees. On some screens there is also Berthilda the witch to avoid and if you take too long on a screen a swarm of bees periodically appears and disappears.

The Gem Eaters can be killed by running into them, but only when they are in the process of eating a gem. While they are moving they cannot be killed. Bentley has the ability to jump and the trees can be stunned for a few seconds by jumping over them. Berthilda can be killed if you run into her while you are wearing the witch's hat.

There is also a honeypot located on the screen and this can be collected for bonus points.

There are secret warps located on various levels, and activating these will jump you several levels forward and award large points bonuses. The first is activated by standing at the rear corner of the first screen and jumping and warps you to level three.

To kill the Gem Eaters, watch them while they are eating gems. Run into them while they are digesting a gem and standing still to kill them.

Do not jump into the corner of the screen when Gem Eaters are close as they will run beneath you, and you will land on them and lose a life.

Make careful use of the elevators to get up to the upper levels and clear them while no adversaries are close. When they come up to join you, drop back down to clear the lower levels.

You can collect the witch's hat by jumping over it. You are invincible while wearing it and the effect lasts for a few seconds.