Received this cover back from the US Amundsen-Scott South Pole Station a short while ago. The South Pole station is within a short distance of the actual south pole. The ice drifts a bit so the exact location of the base is always changing. Originally the base consisted of a large dome under which was housed most of the bases facilities. But a new base was finished in 2003. The last remnants of the old dome have just been removed (Jan 2010). Some images of the destruction of the dome and construction of the new base can be found here.
Project Ice Cube is a "device" to detect muon particles. Muons are the result of neutrino collisions with other particles which apparently is an extremely rare event. It’s essentially a detection array that consists of several holes drilled into an area of pure clear ice with stings of sensors placed place down the holes. These holes are 2.5km deep although the array only occupies the bottom kilometer. When muon particles are born they produce a flash of blue light which the sensors in the ice detect. From the data gathered, the direction of travel of the original neutrino that created the muon can be determined which should point back to the source of emission.
The address I used to get my cover to the base was "Postmaster, South Pole Station, PSC 468 Box 400, APO AP 96598, United States". Being an APO means it's just like sending and receiving mail to the US.