I concur with DD and ExA that Thule must be the furthest North, I also was there on 21/22 April 1975 being screened by the great John Stap****. As the inestimable Wiki has it is the
United States Air Force's northernmost base, located 1,207 km (750 mi) north of the
Arctic Circle and 1,524 km (947 mi) from the
North Pole on the northwest side of the island of
Greenland. It is approximately 885 km (550 mi) east of the
North Magnetic Pole. However, Svalbard Longyearben does trump being another 2 degrees north.
In the bad old days we used to do Thule Trainers which made the Nav work for his keep using GiroNavigation (True +Variation = Magnetic, Magnetic + grivation = Grid or some such). As we only went there in the Spring and Summer months the other trick was to avoid drinking until the sun set and go to bed some time before then.
As to going S, we did take part in Operation Deep Freeze mounting from NZ into Antarctica. It must have been about 1972/3 when Scotty R******** took a 36 Sqn crew. Unfortunately, I was not part of it so can give no details but Scotty, if he is on line, could fill us all in.
Separately, there are some 1312 Flt crews who were tasked from either Stanley or MPN to do aeromeds out of the Chilean base at
Teniente Rodolfo Marsh Martin Aerodrome,
ICAO Code SCRM on George Island at
62°11'27"S 58°59'12"W. Again I have no details.
We did also do recce round the South Sandwich Islands
(where we did not land) but would start low level at about
60 S and 27 W which always seemed more than somewhat
remote even if not the furthest S.