Well the north side of the warren is the baddest part of town. And if you go down there you better just beware of spiders in the ground.
The deepest, darkest, and most neglected cavern of Arnak is, as of the start of the campaign, used as little more than the house of a wide, dark, and near-bottomless pit. The pit itself is used as a place for the goblins to throw things they no longer want. (Simply throwing trash outside the mouth of the cave was once tried, and immediately met by several of the bears that infest the cold forest around the goblins. They were delighted, hungry, and very difficult to convince to leave.) The trash of generations of Bloodmoon Goblins has been thrown into the pit with little appreciation of the location’s convenience and even less curiosity as to why the pit never fills up and overflows.
The reason is that a vibrant ecology of carrion-feeding creatures has existed at the bottom of the shaft – and thus the top of the massive dwarven complex underneath. Any number of monstrous vermin were crawling underneath and feeding upon the goblin scraps – and each other – until recently, when another denizen of the depths decided to enlarge a spider’s egg sac. The resulting spider-terror-babies quickly consumed the rest of the carrion ecology (including the extended family) and started in on the trash pile.
The pile recedes downwards for a few days, and then visibly starts to rustle. A surge of Medium spiders then rushes into the north chamber of the warrens, intent on eating everything and everyone. The goblins will quickly alert, organize, and counterattack, but the battle will be extremely dangerous to all of them – and a rare moment of total chaos within the warrens could provide an opportunist with a window. They should eventually prevail, leaving a nearly empty trash pit beckoning them downwards to more sinister depths…