Oslo Torp and Rygge (the Ryanairports) are miles away, but Gardermoen is the main airport and not exactly close - a good 48km. Again, though, there is a (suitably eyewateringly expensive) fast train service to get you out there.

For non-main airports, one that springs to mind was London Manston airport (now closed as a passenger airport) - 76 miles (122km) from central London. It's closer to France than London.