organizedinsanity.net

This is one of the multiple gates between sections of the City... I don't remember exactly which one, but I suspect that it is the Gate of Supreme Harmony. You can see that there is a threshold at the bottom of the opening. These are common in such structures, and are/were believed to be a defense against evil spirits. Supposedly, the more important you were, the taller your threshold was. You must always step over the threshold, never on it. Or else the evil spirits get you. Or something.