The citadel was sturdy and reinforced enough to withstand sieges. The citadel's gates were tough and large. The city inside was quite like any mid-sized city in Qin. Inside the castle, the stairs towards the main stronghold were high and tough to climb, but Ou Ki and others too easy to do it. Inside the stronghold, a large pool for bathing was there.
The first glimpse of Ou Ki's City was shown when Shin and En visited Ou Ki for training. There, he met Ou Ki Army, heavily wounded on their "training". During the arc, Shin and En visited an indoor bath with Ou Ki and a few of his vassals, presumably within the city.