Amnoon Oasis Arena

I have travelled far in my path for ascension. I am not yet ascended, butI have reached the Amnoon Oasis and I am in search of the arena that I expected to find there.

On the map of the world from the Offical Guild Wars Game Guide, I see an arena being within the vicinity of the Amnoon Oasis.
After a few failed attempts to ask my spamming peers, I was not able to find any answers.

What is the deal with the arena at Amnoon Oasis? Have I been lead to false beliefs or is there a special manner in which I can gain entry?

There used to be arenas spread throughout the land. Now they're all centralized in the competition arenas off of Lion's Arch, which rotates randomly through the different arenas every match.