Eight skyboxes for download.

Note from the author:
If one of the skyboxes don't work, it's because you should remove the "stars" below the "enviro_map" from its .dml file.
If the sky looks weird on the top or the bottom (landscape not matching with the top or the bottom), it's because I forgot to rotate the pictures. So you must:
- Rotate to the left if it's the bottom;
- Rotate to the right if it's the top.

You can also use them in your levels, feel free!