Age of Empires Online

Once you reach level 35 with either civilization this special Horde Quest will be unlocked for you. To start it, talk to King Minos in Crete. The quest consists of 40 waves of enemies on a set map which consists of about 3 tiers. Each tier has gold/wood/stone that you can gather as well as some gold and stone hidden by some trees, more or less rewarding people who keep that tier long enough to chop the wood back to them as there are 2-5 that you can reach on either side. The quest starts with a Minoan wall and some towers set up to help with you early defense, although they won't last very long without immediate action on your part. Luckily, you start out with quite a bit of resources (~1k each).

Starting resources or not, this quest is ridiculously hard. However, it rewards you with over 150k xp, 20 Minoan materials of your choice or any of the 3 Wonders, and a large number of tokens every 6 days.

Good luck, and bring a friend if you can... after talking to the 2nd group to clear the quest overall so far, it seems that doing it solo IS impossible (really not hard to believe at all).