"Doom" is a first-person shooter presented with early 3D graphics. The player controls an unnamed space marine—later termed the Doomguy—through a series of levels set in military bases on the moons of Mars and in Hell. To finish a level, the player must traverse through the area to reach a marked exit room. Levels are grouped together into named episodes, with the final level focusing on a boss fight with a particularly difficult enemy. While the environment is presented in a 3D perspective, the enemies and objects are instead 2D sprites presented from several preset viewing angles, a technique sometimes referred to as 2.5D graphics with its technical name called ray casting. Levels are often labyrinthine, and a full screen automap is available which shows the areas explored to that point.