Here's an almost-circular doorway, off the car park at the entrace of the Barracks. Apparently circular doors are a "classical" Chinese architectural feature - but I don't think this is a particularly great example.

Note the circular watchtower just visible above the roof of the building on the right of the picture. This was a standalone tower, seperate from the wall, and can probably be seen in pictures on my third film - which, at time of writing, hasn't been uploaded. You can see it a bit better in this picture, but not much better...