able to find a specific spot where they do not have to move to gain experience, because monsters are constantly spawned but can be easily and immediately killed. In multiplayer maps, a player may be able to reach areas of the map designed to be inaccessible; for example, reaching an advantageous rooftop position and camping other players. A player might be able to fall out-of-bounds of a map where other players cannot reach them. Invisible walls are cited to be level design bugs, and might be "left-over geometry" from an earlier version of the level or an object's improperly aligned "collision box". In some cases, specific mapping tools can be designed to automatically detect problems such as falling "outside" a level, and reaching "stuck" areas. Careful level designers run these tools as the last step before releasing a new version of a level. In most cases, the best way to improve a map is by playtesting it with experienced players, and allowing them to try to exploit any problems. Notable levels Green Hill Zone from Sonic the Hedgehog World 1-1 and Minus World from Super Mario Bros. Blood Gulch and The Silent Cartographer from Halo: Combat Evolved No Russian from Call of Duty: Modern Warfare 2 Milkman Conspiracy from Psychonauts Water Temple from The Legend of Zelda: Ocarina of Time Robbing the Cradle from Thief: Deadly Shadows Inverted Castle from Castlevania: Symphony of the Night Effect and Cause from Titanfall 2 Facing Worlds from Unreal Tournament Dust II from Counter-Strike Anor Londo from Dark Souls All Ghillied Up from Call of Duty 4: Modern Warfare 2Fort from several team multiplayer games See also Online creation Mod (video gaming) ROM hacking List of gaming topics Game tutorial Sources References 1979 in video gaming Computer art Player progress tracking in video games Video game design Video game development Video game terminology