This arena I'm working on has a castle thing in the center of the map with crumbling walls on either side of it. across from that is a U shaped stream with a bridge on one side and stepping stones on the other. in the middle of the stream is some crumbled ruins. On one side of the map is a wooden house with access to the roof and open windows at ground level; On the opposite side of the map is some ruins filled with sand. Throughout the map are trees, roads, lighting and decorations. I will post pictures in a few minutes..
[EDIT]
Decided not to do pictures- Instead I'm uploading a quick walk-through of the arena. It'll be posted on Youtube in like an hour. Youtube takes forever to upload to.
I'm also going to upload the world file in case someone wants to add to it.
Here is the link to download the folder. Just Extract it into C:/Documents and Settings/<name>/Application Data/.minecraft But make sure to back up your current World 3 If you have something saved there.
http://www.sendspace.com/file/rtouin[EDIT]
I Uploaded a video to youtube but it wouldn't accept the format. It is an .avi. So im not going to bother uploading it again cause it took way too long for what it's worth. Just download the World3 file and see the arena first hand.
... and just fyi, not everyone can extract the folder into that file location.. it all depends on your operating system 
I knew there was another way to open up that folder but i forgot.