So next summer I will be making the rounds of the top three Belgian zoos (Antwerp, Planckendael and Pairi Daiza) as well as Beekse Bergen across the border in the Netherlands. The idea of a zoo tour got me thinking and so I will be attempting a two year long European bonobo zoo tour. This is what the itinerary is currently looking like: 2017 = Twycross, Frankfurt, Stuttgart, Ouwehands (when they finally get them), Apenheul, Planckendael 2018 = Vallée des Singes, Cologne, Wuppertal, Leipzig, Berlin The last four in 2018 will all be part of one tour of Germany during the summer of that year, in which I will have a spare day to visit another zoo. Which zoo should I visit in Germany that I can realistically reach from any of those four cities? Also, what other highlights in the various German zoos mentioned here (Frankfurt, Stuttgart, Cologne, Wuppertal, Berlin and Leipzig), plus Planckendael, can people recommend?
The most notable zoo close to one of the four zoos you're visiting in Germany would probably be Duisburg, mainly for its rather unusual dolphin, which I'm not sure if you've seen or not. Other sizable zoos within driving distance would possibly be GaiaZOO in the Netherlands, Alwetterzoo Munster, or Zoo Dresden; all very nice collections, between which I'd definitely have a hard time chosing.
I have been to Gaia and Duisburg before, though not for many years. Would be good to see how Baby (the dolphin) is getting on, and see the gorillas at Gaia once again. Munster and Dresden both sound good, what makes them worthy of choice?
Ouwehands won't be getting his bonobos in 2017 I'm afraid, next year is all about pandas.... Instead of Dresden, I would go to Magdeburg instead, which lies nicely between Berlin and Leipzig and is becoming more and more a very good zoos with many rarities and high quality enclosures, next year easter the new elephant enclosure will finally open...
To answer your question depends on what you would like to see and your main interests except bonobos ( or primates in general ), because you can reach by train a lot of diffrent Zoos from each of this four cities.
Just a small but obvious point: Are you including Tierpark Berlin in your current itinerary? If not that would clearly be the zoo to add, despite the lack of apes
If you had visited Berlin but forgot the Tierpark I think you might have achieved Zoochat meme status! Also despite the successful breeding population of pedants on this site nobody has pointed out that the Tierpark does have apes: A pair of Lar Gibbons plus offspring.