Is there an add in for oblivion for xbox 360 that lets you go to black marsh?

i have saw a lot of YouTube videos and tried all my efforts to get to black marsh do quests there, and such, but i cant seem to do so,so i need to know if there is a game or a add-in for Xbox 360 that expands your map and game so you can go anywhere, i also have the game of the year edition because my friend told i can go to black marsh in it and the other lands. so if you can let me know that would be great i'll check back in two days for answers. thanks!