Sacred Haven of Debauchery

I built it myself and played alone. The interesting thing is that I didn't bother with the interior, so there was only one room inside, but it looked like a real castle from the outside, with turrets and all. Next to it, I built a fortress wall, like in medieval cities, and placed a garrison. Then I would play out a "siege" – I would take a metal ball bearing, throw it at the structure, and assess the damage. The condition was that the projectile could be launched a limited number of times (5, I think), and if all the defenders were knocked over after that, the artillery would win, but if not, the castle would win.