Kleinmarkthalle Frankfurt

This literally translates to "little market hall." There are all kinds of stands serving every kind of food you can imagine. My favorite stand in there was this classic sausage place. It was dirt cheap, and I hadn't ever heard of it. But my basic belief is if you see a line, you should get in it. And that place had a huge line. It's called Frau Schreiber; the sausage there is fantastic. Also worth a visit: this great little Italian place that sells pasta and truffles.