A desert world I used in my old server. It is fairly large and has a bedrock wall around perimeter.
If you somehow break through the wall it is just a plain Minecraft world.
Enjoy!
Its got some dungeons and volcanoes and a secret redstone machine buried somewhere!
There is a mob dungeon next the obsolete portal.

Additional Notes

It is a big zip file (5.05 MB) so it'll take while to download.
Please say if it doesn't work.