First-person shooters have never been popular amongst Japanese gamers, so it may be surprising to learn that there are not only Japanese fans of the Serious Sam franchise, but Japanese mappers and modders as well. In contrast to almost everything else produced for the Serious Sam franchise, maps and mods created by them are radically different. They provide unique themes and gameplay ideas that are not only refreshing, but also incredibly insane. In the case of this level, the overarching idea involves the player in a world of giants (that just happen to use Japanese style architecture) entering the house of one of the citizens and clearing out the infestation of Mental's forces that have taken hold of the domicile. As you might guess, it takes the idea of the incredibly popular de_rats map for Counter-Strike, and ran with it, making a whole campaign out of it.
Yes, I said campaign. To say that this map is large is a massive understatement. It is so big that the author even included a scene-select option that allows you to jump to the halfway point of the map.