It is located beyond Petalburg and a few smaller stone fortresses. The Sun Stone and the Moon Stone are found inside are used to open the pipe to Hooktail Castle. They say that long ago, Shhwonk Fortress was a place of relief from monster invasions for Petalburg residents. Past this, however, monsters invaded the fortress, and since then, traversing to them was actually outlawed without permission from Kroop. The fortress is estimated to be about a thousand years old, and seems to have been built around the time of the Thousand-Year Door.