The Games For Windows Marketplace now offers the promised release of the Minerva's Den DLC for the Windows edition of BioShock 2, the waterlogged first-person shooter sequel (thanks Vor). Here's word on the $9.99 USD add-on:

Minerva's Den offers a brand-new, self-contained BioShock story, presenting a side of Rapture you've never seen before. Seek out the tools you'll need to unlock new goals and spaces in the order you choose. Face Rapture's full range of opposition as you increase in power---a new challenge is always right around the corner. There are no refunds for this item. For more information, see www.xbox.com/live/accounts.