The Wizard's Tower costs 150 Microsoft points on Xbox Live Marketplace, which is around the same as it is in old money for PC owners - $1.89.
The tower's home to a powerful mage who wants you to look after it. In the tower you have an altar for summoning things and creating spells and enchanted items, a garden full of potion ingredients, teleporters to every mage's guild, and a bed to sleep in.
PC fans can download it from Obliviondownloads.com, while Xbox 360 owners can find it through the relevant Marketplace menus.
Meanwhile, PC gamers without DirectX 9 compatible graphics cards finally have some way to play Oblivion - a project called Oldblivion will patch various areas of the game to support a number of older graphics cards.
More details and download links can be had through the Oldblivion website.