When associated with a castle, it most often consists of high hedges made of different designs, a labyrinth if you may. They can be entered, but it is difficult to find an exit. Hedges are made up of different plants. Yew is a common hedge plant. Mazes are not restricted to hedges.
Common materials used include bricks, logs, concrete, stone, and gravel.
Also, while not all mazes are high, they are as difficult to find a way out as over-eye level mazes. Listing of Castles with mazes. The origin of mazes seems somewhat cloudy. There are traces of mazes that go back to pre-history, usually depicted as spirals. It has 3000 chambers and a forest of pillars that made it impossible for intruders to find their way in or out of the temple.