You are probably right about the multithreading thing. For example, when you go to another level of a dungeon, the game probably loads only the part of the map that you can see on the screen at that time. Then some sort of thread is started, which runs next to the game thread, so you can play the game already. This newly created thread starts loading the map: it begins with the area close to you (only a few times the screen width for example), and as it continues it loads parts of the area which are further away, until the thread has finally loaded the whole map. Because this thread takes up too many cpu-cycles sometimes, there is not enough ''cpu-power'' left do run the game thread properly; that''s why the game can run ''sluggish'' when you enter a new level of a dungeon.