This letter came back to me from The Alfred Wegener Institute of Polar and Marine Research in Bremerhaven, Germany. It was sent down to Neumayer Station III where the stamp in the left corner was applied (or so I was told). It was cancelled aboard the research icebreaker RV Polarstern before coming back to me through 'regular' postal channels.
Neumayer III is a modern research base and has only been in operation for a couple of years. It sits on the Ekström Ice Shelf which is moving towards the ocean at a rate of 200m per year. Six meter tall hydraulic stilts keep the base above the accumulating snow. Here is a webcam shot of the Neumayer III.