You have followed a dummy link. A link to Unknown simply means someone did not know the correct information to include in the page, or such information has never been made available by official means. This is done so that it is easy to find these items later, should someone else know it, or it become officially known.
For a list of pages containing unknown tags, click here. If you know what the information is, edit the page and replace the
[[Unknown]] tag with the information, linked if appropriate.