This is not a map, but a massive collection of skyboxes for level authors to use. The collection was put together by Speaker and contains over 240 skies. Included in the download is a simple map to help authors test the skies and a gallery which contains a single shot of each sky. Both items are very handy when searching for a sky to use.
The download on ..::LvL and mirrors is for a single zip file of all skies and is over 450MB.
If you are more interested in downloading individual skyboxes, grab the galley file (9.4MB) and download the individual releases from Speakers site when you require them.
Speaker has done a great job collecting all these skyboxes. This is a valuable collection for all mappers.
Update: Speakers website appears to have vanished, so the individual download option has been removed. (28.Nov.2010)