DM ran us up against a Terrasque. 2nd edition rules. Basically we had no way of defeating this thing as it rampaged through the countryside.
One of the players had a Daerns Instant Fortress. We put it into Otiluke's Telekinetic Sphere, and started smacking the Terrasque in the nose with it. It snapped at it, bit down on it. Then we triggered the command word. Instant 50' iron tower. Did the reduction command, made it small again, repeated the process, then beat on it until the mage could finish his Wish spell to finish it off.