iirc Mehrunes Razor, fighters stronghold, theives den and wizards tower are only available through xbox live and as some kind of steam bundle now. I dont think they were ever available to ps3 versions of oblivion which is why itd be amazing if there was ever remake of the game. Most of them just add houses but a castle is always going to be better than a waterside shack. And you have access to enchanting and spell making without the monotony of joining the mages guild. But you can do that on the pc with console commands anyway