Link to thread on Uncharted 3 Playstation Forums
http://community.us.playstation.com/t5/Multiplayer-General/Fastest-way-to-get-Co-op-Arena-treasure/m-p/36963446
1. Match settings
To get started, create a custom game and select Chateau as the map. For the difficulty, select Crushing (It could work equally well on other difficulties, hasn't been confirmed yet though). It can be done with 2 or 3 players, we recommend 3 players for maximum effectiveness!
2. Siege in round 1
The next step is to get Siege as the first mode. If it's anything else, quit and restart until you get Siege. Once you have Siege on round 1 you need to check the capture territory is behind where you spawned. There's 3 possible territories in Siege on Chateau, as long as it's not the one in front of you as you initially spawn by M-32 Hammer and cars you are good to go. If you get the territory in front of you, kill yourselves and reset the territory until it's behind you.
3. Flipping the spawn
Now that you have the correct Siege territory, head over to it and kill 7 enemies, this is important, kill 7 enemies so you have 18 remaining in the bottom right corner. What you will notice is that once it hits 18, the enemies will start spawning on the other side by the M-32 Hammer and cars, so all players run over there!
4. Controlling the spawn points
The enemies will now start spawning in 3 different places, each player has to take a different spawn point and control it. Use the diagram I have created below to see where each spawn point is.
5. Kill, kill, kill...
An infinite amount of enemies will drop down from these areas and all you and your buddies have to do is stand there and kill them as they drop down. What's so good about this strategy is you are playing on round 1 so only easy enemies will spawn. The huge pile of bodies in front of you also means you never run out of ammo. Essentially the game will never end as you are playing outside the Siege territory so the kills don't count down, but enemies still drop treasure.
Music
Morgan Page - The Longest Road feat. Lissie (Grifta Remix)
