New Zealand’s Whangarei Aerodrome and Morocco’s Tangier Ibn Battouta Airport are on precisely opposite sides of the earth: In an antipodal map projection, which maps each part of the world to its opposite location, the two airports’ runways even cross.
Unfortunately, at 1,097 meters, Whangarei’s longest runway is too short to accommodate a commercial jet with the necessary range, so there’s no way to actually fly from one to the other. For the dedicated air traveler, the next best pairing is Taipei and Asuncion, which are 19,912 kilometers apart.
02/28/2022 UPDATE: Wait, I’m wrong — a reader tells me that on an antipodal projection the closest points on the two runways are about 23.8 kilometers, or 14.8 miles, apart. Still, remarkably close!