can anyone explain to me what just happened? People in here say it's a reference to Minecraft (I don't play the game so I don't get it)
In Minecraft the monsters are forbidden from spawning too close to a player or near light sources so usually the game chooses a platform that's large enough near the player and without much light. Players manipulate these odds by building well lit high platforms and above them enclosed rooms where the monsters spawn. Said monsters then slowly walk towards a hole(or are forced to move with carefully place water tiles that pour towards that hole). Then they usually end up in a constructed "kill" room. Where the players can hit them without getting hit themselves and thus farm EXP and items.
In the manga now.
The protagonist created a building that affected the spawn location of the monsters. I assume they are programmed to spawn as close to the town as possible but not IN the town.
So I assume when she built that tower she created a "perfect" monster spawn location that is as close to the town as possible, but not be considered the "inside" of the town (since it's so high up),so whoever programmed the game never considered that such a location could be so high up, that the monsters would die as soon as they touch the ground(that, or the monsters were supposed to hit "the sea" and as such not take any fall damage).