That bridge in the southwest part of Mor D'hona that leads to Thanalan... there's land under it, but the bridge was designed to pass over it and into Thanalan. Very likely, if we had access to the whole map, it would be possible to walk under that bridge. The rest of Mor D'hona hasn't been inexplicably removed, the bridge (built by the Empire to boot) simply circumvents it by passing over it.