Couple of years ago a whole Spanair scheduled service MD-80 flight from Madrid to Santiago, Northern Spain flew the opposite direction to Seville, Southern Spain, instead. Everyone on the commercial side thought it was going to Santiago, everyone on the operations side thought it was going to Seville. Aircraft had been sub-chartered in from FlyNordic, a Scandinavian charter operator, on a damp lease, with a non-Spanish speaking flight deck crew, so the Spanair cabin crew made all the normal announcements about Santiago to the passengers. Somewhere along the way between Spanair and FlyNordic ops the error was made.
Preceding flight had also been a round trip to Seville, crew just had it down in their paperwork they were doing a second one. Cloudy all the way so no passengers noticed an unusual direction ...... you can guess the rest. ATC had them down for Seville in the flight plan as advised by ops, which the crew flew, but when they arrived nobody at ground handling was expecting them.