AUH, BRU, DXB, YUL, ORD, IAD, MUC, FRA, ZRH, JNB, LHR, LGW, MAN, BAH, RUH, TLS, CBG ..... and probably quiet a few more I've happily forgotten about.

CDG and DFW seem to be popping up a lot, and they're about all I can think of for myself.

As far as I can remember:

ATL Atlanta
CLT Charlotte
MAD Madrid
PIT Pittsburgh (back in the days when it was US Air's main hub)
RDU Raleigh
RIC Richmond (it's not a major hub, I know, I was just flying AA LGA-RIC-DFW)

AMS Amsterdam (LHR-AMS-FUK, FUK-AMS-LHR)
HEL Helsinki (LHR-HEL-FUK)
FRA Frankfurt (LGW-FRA-NRT, BHX-FRA-NGO, KIX-FRA-BHX)
NRT Narita (LHR-NRT-FUK-NRT-LHR)
NGO Nagoya (FRA-NGO-FUK)
HKG Hong Kong (TPE-HKG-LHR)
PEK Beijing (DLC-PEK-LGW)
KIX Kansai (FUK-KIX-FRA)
DLC Dalian (FUK-DLC-PEK left aircraft, same flight)
TPE Taipei (FUK-TPE-HKG left aircraft, same flight)

FRA, ICN

LIM, MDE and CLO.

I have not left the airport in SEA, PHL, CLT, and PHX

NRT and technically SZX although we were in the suburbs transferring from the North Station to the more populous Bao'an County where the airport is

IAH (SFO-IAH-MCO-IAH-MCO)
NRT (SJC-NRT-MNL-NRT-MNL)
BOS (SFO-BOS-LHR)
DFW (LGW-DFW-SFO)
FRA (SFO-FRA-LJU)
ARN (OAK-ARN-CPH)
OSL (OAK-OSL-ORY)

YVR and SAN come to mind as two whose cities were destinations in my youth, but to the point I that don't remember too much from those trips, but as of late have used as connecting airports without visiting the city (YYC-YVR-SFO in 2013 and BWI-SAN-SFO in 2015). That said I'm still hoping to visit Vancouver with a friend sometime in the future, however my chances of having a reason to visit San Diego have come and gone somewhat since the event that I had capabilities to attend the last two years in early January isn't coming back for January 2018.

Airports I've visited purely for aviation enthusiast reasons and never left the terminal complex or immediate surrounding area: SIN, YYZ, YUL, ARN, OSL, FRA, BKK, ICN, OTP. I've also flown through numerous US cities purely for the same reasons at one time or another but at other times I've visited the cities.

I've connected through LAX, SFO, IAH, IAD, ORD and YYZ without stopping to visit the respective cities. I also connected through YVR and EWR without stopping a few times before finally deciding to visit the respective cities the airports served.

Oh plenty of them:

I used to be a frequent traveler to Pakistan when I was a youngling.

Never left the airport:
DXB Dubai (going EK to LHR from KHI)
DOH Doha (going QR to KHI from ORD)
AUH Abu Dhabi (going EY to KHI from ORD)
FRA Frankfurt (back when LH flew to KHI)
LHR London Heathrow (there was no DXB-ORD flight at the time so we stopped in LHR after DXB. LHR sucked!)
MAN Manchester (When we used to fly PK on KHI-MAN-ORD)
ATL Atlanta (When on a layover from IAH to ORD on DL)

I have a lot of hubs I have flown through but not visited the city:

ATL
BWI (If you consider Baltimore and Washington as two distinct areas)
CLT
ORD (I want to visit Chicago but never have the opportunity)
ZRH (never visit switzerland but visit

Departure airport that I flown several time from it but never visit the city: ALB

MUC, DXB and SFO.

On account of the people at MUC airport who were super helpful and the extremely friendly passport control staff, it's a crying shame I didn't get to spend time in Munich. DXB airport was efficient enough to go through, but I'm not sure if I really wanted to see the city.

HKG - transfer from QF to AZ
FCO
LHR (twice - once in the old T1 transferring from AZ to BD, once transferring from T1 to T3 transferring from BD to SQ)
SIN

cpd wrote:

DXB airport was efficient enough to go through, but I'm not sure if I really wanted to see the city.

Unless your idea of fun is huge, overpriced, malls you haven't really missed anything. Burj Al Arab? Eyes need washing with bleach afterwards, and it takes 'overpriced' to a whole new level. Wild Wadi? There are far, far better water parks around - you could miss this and not miss a thing. Burj Khaliffa? If you're lucky with the weather, sure, there's a view. Of skyscrapers and an empty desert. Chances are, however, visibility will be crap and, once again, you haven't missed a thing. Atlantis? It's a hotel with an aquarium. Wow ...

The Cyclone used to be fun, but it's been closed for a fair few years now.

Kuwait (couldn't leave airport becaue of my Israeli stamp in my passport), Bahrain (they wouldn't let me out even though I had an 8 hour stopover), Amman (my girlfriend needed a visa so I stayed airside with her), Muscat, Orlando, Chicago, Los Angeles, Miami, Philadelphia, Ft Lauderdale, Panama, Brussels, Paris CDG, Bucharest, Moscow SVO, Kiev Borispol, Rekjavik, Dallas DFW, Zurich, Madrid.

Not that many, considering how much I've travelled and many of these places I have visited at other times. Once I flew via Brunei and when I landed there I found the airport looked so interesting that I went to the ticket desk and changed my ticket so that I could stay a few days. Iceland, Oman, Kuwait and Bahrain are places I would have liked to see. I have passed through Chicago more times than I care to remember, but never saw the city. It takes ages to get through there from international to domestic - 2 hours is barely enough.

The quickest transfer was at Zurich, where I was amazed by the efficiency. I had a connection time of 25 minutes which turned out to be plenty of time. Within 5 minutes I was through immigration and at the gate for the next flight. Orlando, on JetBlue was also a very quick and easy connection as were Amman and Kiev. Kiev was very clean and modern, with good local food at reasonable prices. Kuwait was overcrowded and had a severe shortage of toilets - where you might expect to find 10 stalls, there was 1. Moscow SVO was horrible - I spent 4 hours sitting on a stairway with no view of the outside world. It was either that or pay 5 Euros for a capuccino in a windowless room with no natural light. Rekjavik had long queues because all the flights land and depart within a 2 hour window in the middle of the night. It was funny because I got talking to a guy and he asked me "what do you think of Iceland?" I don't know, it looks dark, rocky and cold! Muscat was kind of mysterious - there were big 747s belonging to the Emir, lots of beatiful villas on the raggy coastline and the airport itself was old fashioned but clean and efficient, with some kind of strange tower attached to it. The temperature was about 50 degrees when I was there.