Out of the 50 zoological facilities I have visited so far, there are six that have since been closed - although two of these were connected to other kinds of facilities (nature reserve and museum) that have remained open and continue without the captive animal holdings and displays.
Vogelpark Zwin (Knokke-Heist, Belgium): This was a small and pretty outdated/worn-out bird park with mostly birds native (or previously native) to Belgium and Western Europe, next to a large nature reserve. The bird park has since closed and been demolished to be replaced by a new education center and the "Zwin Nature Park", a nature experience park with small-scale replicas of tidal and dune landscapes. The nature park does still house the European white stork colony that was previously part of the bird park, but all captive birds were moved to other zoological facilities. The nature reserve still exist and has in fact been substantially expanded recently.
Vlindertuin Knokke-Heist (Knokke-Heist, Belgium): Butterfly garden in Knokke-Heist - Het Zoute. I don't remember very much about this place to be honest as the visit happened quite some time ago and there isn't that much information about it that I could find. It was kind of nice, as butterfly gardens usually are, but it wasn't anything more and it was pretty small, so I would say it wasn't all that much to speak about and not really a loss, especially considering butterflies are now sometimes part of the collections of zoos.
Aquatopia (Antwerp, Belgium): Aquatopia was located within the massive Radisson Blu Astrid Hotel Antwerp, which is in fact located on the opposite side of the square (Koningin Astridplein) that also houses the entrances to Zoo Antwerpen and the magnificent Antwerp Central Station. The aquarium was closed because of declining visitor numbers and revenues and disinterest of the new owners of the hotel chain. Aquatopia's former location has now become a chocolate museum/experience center named "Chocolate Nation" (I do like chocolate, but I still think an aquarium was better use of the space).
The aquarium was actually quite nice with a decent collection that also included some herps. But in places it was also rather tacky - I mean, a Maya temple themed area with piranhas, or an escalator passing through a huge mock-up of a great white shark's mouth while the (in)famous music from "Jaws" played, anyone have another term for that than tacky? And while it was nice, a visit there never lasted all that long, even if one tried, and it was quite expensive for what was offered, certainly when one compares it to aquariums within zoos. Some areas of it were also a bit cramped and possibly noisy, especially on busier days.
I do however think it was a loss to Antwerp and the zoological world to see Aquatopia closed and I do slightly regret not paying a final visit before its closure.
Museum Koninklijk Belgisch Instituut voor Natuurwetenschappen (Brussels, Belgium): Museum of the Royal Belgian Institute of Natural Sciences, our national natural history museum, located in the European quarter of Brussels, not far from the European Union and European parliament buildings.
The museum very much still exists, but to my knowledge and research there are no living specimen exhibits currently. It used to house some aquaria and a vivarium room with mostly invertebrates in their entomology and malacology halls, but these have been definitively closed as part of the museum's ongoing renovations and re-developments. With this and the ending of a temporary exhibition on poisonous and venomous animals including living specimens, they don't currently display living specimens, although they likely do have some, somewhere, for research purposes.
The living animal exhibits were small and modest but interesting nonetheless. I'm not sure whether the museum will have any living specimen exhibits in the future after the re-developments, and while living animal exhibits would certainly add something to the museum and be helpful to its educational mission, it could still function very well without.
Dierenpark Emmen - Emmen Zoo (Emmen, the Netherlands): The old Emmen Zoo that was replaced by the controversial Wildlands, which I haven't visited yet. While the old Emmen Zoo had its issues and downsides due to the constraints of being on a relatively small space within city limits, it was still a fairly nice zoo with some pretty nice exhibits that I really did enjoy during my visits. I also had my first visit to a very young baby elephant at Emmen.
I liked the old zoo and hearing what's happened to the location since has been a bit disheartening (decay, vandalism, demolishing of building, new developments lagging). Wildlands is very, very different to the old Emmen Zoo and I think it's kind of regrettable that some of the old flavor and characteristics of the Emmen Zoo went lost in the new concept, which seems to not have worked out all that well so far, or at least not as well as hoped or expected.
Dierenpark Wissel Epe (Epe, the Netherlands): This place was closed after the 2015 bankruptcy of the Zodiac Zoos organization. It was taken over by Libema (owner of Safaripark Beekse Bergen and Dierenrijk that took over Wissel, Zoo Parc Overloon and AquaZoo Leeuwarden after Zodiac Zoos went out of business), but Libema saw too little opportunities to expand the small place and found the size and quality of the exhibits too low to continue, so the animals were moved out and the place closed, while Overloon and Leeuwarden did continue to exist and have substantially developed since.
Wissel did have a nice collection with some interesting and rare species, some of the exhibits were definitely not ideal or great (although some were okay or quite nice too). It's sad that plans to expand and improve the place that once circulated could never be realized, and it's a bit of a loss that the place is no longer there. However, the Dutch zoo landscape is still very well filled and the place as it was isn't missed all that much amongst all that is still there. Even if the place had been given a future, who could say it would actually have worked out in an already very full market?