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!
Modding Oblivion requires a lot of playtesting to check that everything is alright. The playtesting phases are a lot more fun if you use a nice character to do it too. This is my latest character visiting Port Constanze which is currently a new town being built. She's of course a Hidden Elf by Korana, the best race for female characters I've come across. I swear by it. Tesnexus.com