When and how long you planning on staying? For example if you're going this summer I'd suggest a club like Oase or Sharks that has large gardens and pools, you might think why, as you're there primarily for punting, but it's nice to have something to do in between sessions, so a club with good outside facilities is a positive on a hot summer day, I was in Frankfurt last summer, and I did Palace one day followed by Oase, found Palace to be very quiet, think because it's a club with no garden a lot of punters and girls stop coming and move to other clubs in the summer months.
So Frankfurt could be a better idea in summer, Oase and Sharks are outside Frankfurt, Sharks is in nearby Darmstadt but use trains to get there, if you're not to bothered about gardens and pools try Düsseldorf, club to check out would be either Oceans, Magnum, Dolca Vita, or Koeln is only a short train ride away, so you could spend sometime there too, Samya would be a good choice, or the laufhaus's like Pasha and Das Bordell on Horn Strasse.
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