Dibella's Watch adds an entire new continent to Oblivion. It comes complete with a major city, castles, towns, villages, farms, monasteries and all the good stuff that makes up a Medieval landscape. There's also fighting to be had and quests to be made!
The City is the Capital of the Island, although the county based there only really has control over the civilized eastern parts of the island. The rest of the island of Dibella's Watch is under the control of feuding medieval counties and trade colonies and western clans of barbarians.