There are plenty of festivals and other events in Berlin, especially during the summer, when the weather is relatively good. One of them is the Berlin Beer Festival, which according to the Guinness Book of World Records, is the longest beer garden in the world. It happens during a weekend in August, in the eastern part of the city, in a stretch of a road that spans 3 metro stations. If you are a beer fan, then this place is something to visit for you.
More than one hundred breweries come down and showcase their beers. There is actually a specialized 0.2 liter glass mug just for the event, so that you can try out several different types without actually drinking too much of one type. There is a large showing of German beers of course, but there are also plenty of other international beers. And yes, there's not only beers, but also festival food. So it can be some interesting thing to do during a weekend.
I've been to this event twice now, the first time was two years ago, and again this year. To be honest it is not really my thing, since I do enjoy beer but I don't really like the crowd that comes with it. However, it is also a venue to discover new things, like beer from Estonia, or beer from Iceland, or beer from Laos. At least it gives me ideas about what is out there that is available. And of course if you have friends who want to walk along a long beer garden while sampling several different types of the drink, then this is the optimal place to go to.