My vote is for departures from Milan Malpensa (MXP).

Mrs. ND76 and I overnighted in a nice hotel near Milano Centrale (the main railway station), and took an early Malpensa Express train from Centrale to MXP. I'm guessing that we walked at least 500 meters (the walk was under cover) to get to an elevator which took us to the check-in counters level of Terminal 1. At that point, we had to walk another 500 meters or so to check-in counters 20-24 at the left end of the building. All the USA airlines and El Al are back there. We arrived at the corridor leading to these counters around 0840, and security would not let us go on to the counters unil 0900 (our MXP-JFK flight was scheduled to depart at 1200).

Once check-in was completed, we had to walk back at least 400 meters to reach the security entrance. Oddly, security was a relative breeze, as we got through that in less than 15 minutes. Once past security, we had to walk another 400 meters or so through the duty free shops and concessions until we got to passport control. Once again, this process was largely automated, with self-scan passport gates (although we had to report to the border police to have the passport stamped). After passport control, we had to walk, I'm guessing, 600 meters to get to gate B79, Delta's departure gate. The only concessions between passport control and B79 was the Montale lounge almost immediately after passport control, a small duty free shop at the entrance to the gatehouse which contained B79.
and one coffee bar opposite B79

We were not in Delta One and didn't have Delta/SkyTeam access to Montale, but the agent who checked us in suggested that we might be able to get in on our AMEX cards. He was wrong. The only cards Montale accepted were Priority Pass; and we were not offered an option to pay our way into the lounge.

I can't remember being in an airport which required so much walking and was laid out in a Rube Goldberg style. Are there other international airports which are more difficult to navigate than MXP? Interestingly, it was relative easy to leave MXP; we had a decent walk to the immigration and customs area, but we got through those easily and our bags came onto the carousel quickly.