Biggest Flea Market in
Why locals love it
The Flea Market in Sachsenhausen along the Main river is the most popular one of all flea markets in Frankfurt. Every second Saturday it takes place from 9 in the morning until about 2 p.m. A lot of people spend their whole Saturday morning there. Of course, the real "hunters" already come at 6 a.m when the vendors are building up their tables.
Why you should visit it
Just wander around and explore all the things the vendors have to offer. There are some "professional"/commercial vendors and of course the private ones who just want to get rid of their odd stuff.
Afterwards you can visit one of the many museums that are located on the same street as the flea market.
The location alternates between Sachsenhausen and Ostend (Lindleystraße) every 2 weeks. But I find Sachsenhausen has more ambience and flair.