Gday Loco,
I was lucky enough to crew one of those NYE Antarctic charters a few years ago. The sightseeing part of the plan is kept deliberately flexible. On the way down the crew establish contact with the various bases to determine which part of the continent will provide the best viewing. The preflight sat pics provide a good starting point but the weather down there can change so quickly it is necessary to get live updates.
As to the altitude, we didn't get below 18000', but it depends on the area of ops.