Ballista Tower is a compact two-level fortification built around a single oversized weapon. Stone rooms, narrow stairs, storage spaces, barrels, bunks, and grated sections support the tower's military function, while the upper position and mounted ballista make control of the structure immediately valuable. The surrounding ruin and vegetation keep the tower from feeling like a pristine fortress.

For a GM, the siege engine creates an objective before any creature is placed on the map. Characters may need to capture it, disable it, defend it, or survive fire from it while climbing through the tower. Tight interior spaces contrast with the exposed firing position above, and the stairs provide a natural choke point between the levels. In Tyrant's Grasp, Ballista Tower fits the military locations of Last Watch; elsewhere it works as a border fort, ruined gate tower, watch post, or battlefield emplacement that can change the balance of an encounter if someone manages to bring the weapon to bear.