I was in Munich airport for 7 hours yesterday but unfortunately (and somewhat surprisingly) it's pretty difficult to visit the zoo in that time.
I only did it once - long ago. It was a layover in Las Vegas, Nevada. I took a cab to the white tiger habitat at The Mirage Hotel. Did not have a lot of time but of course did not need much time for one exhibit (this was before they added The Secret Garden in back). It was also before the attacks of September 11, 2001 that forever changed airport security. Back then you did not have to go through security you could just walk up to the gate (whether you were booked on a flight or not). Now, with the trouble of airport security, I would never leave and re-enter an airport between flight legs.
Some asked about transit at a US airport! I think for the most part, it is possible, but really stretching it. And something I would normally not recommend unless the layover was at the very least, 10 hours, if everything goes right! Personally, I never tried it yet!
We did this in Madrid. It's a relatively straightforward subway ride from the airport to the nearest station (in my recollection about 30 mins) and then an easy 10 min walk to the entrance.
I'm quite surprised about this fact too - having been to Munich recently I reckon you could easily get there by the Bahn network in just over an hour from the airport.
As was I. My initial stopover was due to be for 2h but due to a brake fluid leak noticed in Egypt, the initial flight was delayed and so I missed my plane back to Manchester. It took about an hour to organise tickets on the next flight and because I had to work a night shift that evening I really couldn't afford to miss it. I was therefore advised to leave at least 1.5 hours each way to get to the zoo, and I'd need to be at the airport 2h before my flight. That meant that I'd end up with just one hour at the zoo. With the bad weather, transport costs and the limitation of zoo time I felt it wasn't really worth it and so I just loitered around the airport's cafes.
In Greece, Attica Zoo is indeed a suitable airport transit zoo, the only issue is the taxi fare. Taxi is the easiest and fastest way to get between Athens International airport and the zoo, but taxis at the airport are expensive, having waited for up to several hours for their next customer. *However, the zoo has a discount agreement with a local 'luxury' company called Taxiplon; any routes beginning or ending at the zoo receive a sizeable discount. From the zoo to the airport is €20, and to the city centre around* €25-30 depending on your destination. In contrast other taxis typically charge* €30 from the airport to the zoo. The phone number for Taxiplon is 210-2719555; the airport information desk should be happy to call them, and the zoo can arrange the return trip. The zoo is large, so any transit visitors will need to prioritise what they want to see, but if there's a monk seal on display I'm sure that'll get adequate priority. The journey takes between 12-30 minutes depending on your driver's knowledge of the routes, and any road closures (a farmers' protest had closed some major roads when I visited). Taking buses is another option, but with several changeovers it's not too practical for the visitor who needs to get back on time.
The Minnesota Zoo is about a 15 minute taxi ride from the Minneapolis/St. Paul international airport, and as a "hub" it is actually a place where you might be waiting a few hours for a connecting flight anyway. Totally doable if you have 5 hours or more.
On my recent trip, I engineered a 15 hour stopover in Hong Kong, arriving at midnight and leaving at three in the afternoon. I caught a surprisingly good 40 winks under a bench, then caught the first subway to the city in the morning (at 6.00 a.m.). This takes 40 minutes and then it's a 20 minute walk uphill to the zoo and botanical garden (different from Ocean Park), which conveniently opens at 6.00 a.m. as it is also a public park. You can easily get around the zoo in two hours and then you find yourself in the centre of Hong Kong at 9.00 a.m. with the morning ahead of you. Pretty good! Actually the zoo itself isn't all that but it is a nice way to start off the day. Also the timing means you have a decent shot at watching the sunrise, although I didn't find a spot to watch it through the buildings of the financial district
Schiphol airport I've just spent a few days based in Amsterdam and it's now the tram number 9 from the station to the zoo. Unfortunately I discovered this for myself several times this week. I made a return trip from a zoo to Schiphol airport on Wednesday, and I actually chose Avifauna. Nice and easy; the 370 bus goes directly from the airport to a stop a few minutes' walk from the zoo. 13 euros return, about 35 minutes each way. The park takes a few hours to visit properly, but most of the highlights can easily be seen in a couple of hours.
On my recent South American trip I visited a few more zoos whilst on transit. Bogota, Colombia - Bioparque La Reserva and Parque Jaime Duque (+Salt Cathedral): A trip which really needs a taxi to be hired for the day and you'll need to have directions available or the driver to have a GPS system as they struggle to find La Reserva. Bogota evening traffic is horrendous, so I almost missed my onward flight. 24h left luggage facilities in the airport are near domestic arrivals. Santa Cruz, Bolivia - Again, a taxi is probably needed to visit this zoo which is around 35 minutes' drive from the International airport. Left luggage facilities at the airport. Parque de las Leyendas, Lima - The zoo is conveniently located half way between the airport and the city centre. There is a left luggage facility at the airport (head into domestic arrivals). Once more, taxi is the best way to access the zoo. Typical cost is about 20-30 soles. Buenos Aires, Argentina - Across the road from Jorge Newberry Airport (Aeroparque) is the Club de Pescadores, which has a small aquarium within. Although it sits on the sea opposite the airport complex, it's about a 20-minute walk from the airport exit. If you choose to take a taxi then do not get it from the airport taxi stand; cross over and go out to the main road (near the bus stops) and hail down a passing taxi - using the meter (fare 1) they'll only charge a minimum fare [roughly 15% of what the waiting drivers would quote]. Curitiba, Brazil: The airport and zoo sit to the south of the city; surprisingly it still takes about 30 minutes to get from one to the other and taxi seems to be the only way. Passeio del Publico, the old zoo, sits in the city centre and so transfer from the airport should be easier. Be aware that neither has an entrance complex or facilities for left luggage. The airport has a service with limited hours (lockers attended from roughly 9-3 on weekdays and Saturdays, but no Sunday service) Villavicencio, Colombia: The small airport caters for flights mostly from Bogota, with the last departure shortly after 5pm so I don't think it's much of a 'transit airport' but the zoo (Bioparque los Ocarros) is a couple of minutes away in a taxi so it's an easy trip should you find yourself near here. Visits from which I've gone directly to/from an airport or which seem like practical transit zoos: Guarulhos Zoo, Brazil - about 20 minutes from Sao Paulo's busiest airport is this small, free zoo which houses a number of interesting animals. Again, a taxi would be required to visit and it's probably best if you ask them to wait for you (depending on price). A visit to the zoo doesn't take too long. Alternatively the cafe outside the zoo is now able to call a taxi for you if you choose to request another for the return trip. There is nowhere to leave your luggage at the zoo. Iquitos, Peru - both CREA (Amazonian [manatee] rescue centre), and Quistococha Zoo are further out of the city on the same road that passes the airport. It seems quite straightforward to get a mototaxi and head down to either/both collection(s). Guira Oga rescue centre and Biocentro, two separate collections in Puerto Iguazu in Argentina both seem like practical airport trips - again I think taxi is the easiest way, with a taxi costing less to the zoo than to the city centre. Bus is also an option, but involves a changeover in the city centre. Be wary of closing times (last tour is usually at least 1hr before closing). Parque Das Aves, Brazil - Just across the border from Puerto Iguazu is Foz do Iguacu in Brazil. The road out to the Brazilian side of the Iguazu Falls goes out of the city for several kilometres before reaching Parque das Aves, the airport, and the falls quite close to each other. It's certainly very easy to cross over to the bird park from the airport but I'm not sure that visitors will be so keen to potentially miss out on seeing the falls.
Having recently travelled from Aquazoo Dusseldorf directly to Dusseldorf airport (roughly 30 mins by public transport), I can confirm that it seems a good candidate for an airport stopover zoo trip. Unfortunately it was still closed for renovations when I'd been planning flights via Dusseldorf in the past.
I did the Denver Aquarium on a layover there. The aquarium is open late, usually until 9 I believe, which gives lots of opportunity. The zoo is a bit closer to the airport, but is obviously much larger, and flights usually get in around closing time or later - gates close at 4pm year round - so the zoo is nearly impossible.
I've recently had two stopovers at the new Istanbul airport (which has replaced the now-closed Ataturk airport). Unfortunately its location and poor transport links make it much less suitable for transit zoo visits than Ataturk. The airport still doesn't feel ready, with no metro access, no WiFi, poor signage, poor shop selection... All in all, a frustrating change but I hope it improves quickly! In order to get around on my first stopover I had to hire a taxi for the day. Despite a delayed connection, it was too risky to leave the airport on my second stopover.
