It is the biggest festival on earth. Around 6 million people drink around 6 million liters of beer in only about 2 weeks. It is also the biggest meat market in Germany - both eating- and dating-wise. And everything takes place on this ground.
Admittedly, if there is no event taking place at the time of your visit, this festival ground doesn't look like much. But there is always the chance that there is something happening. In summer sometimes there are also flea markets. And yeah, there is Oktoberfest as well. And if not, just head to the big statue called "Bavaria".
During the construction of the Oktoberfest tents you can get a really cheap lunch in the canteens for the construction workers.