The Donjon of Andernach.
One of the most visual reminders of the 9-year-war is the Round Tower of Andernach, its donjon. After the french army sieged and captured this city they destroyed many of Andernach’s city defences. Its favorite way of doing so was by using explosives.
The French placed the explosive in the wall of the donjon and lit it. However, the Donjon survived. After that the French did not try it again. The attempt is still visible today.