In the location's words:

Every Saturday (except on public holidays), the Frankfurt flea market opens its doors at Schaumainkai or Osthafen 1 from 9 a.m. to 2 p.m. Here you can browse through all kinds of junk, second-hand goods and handicrafts, enjoy the impressive Frankfurt skyline or the rustic charm of the Osthafen and take a leisurely break with a snack in between.