Well, they sorta unplugged.  The show was electric, they just did it without a sound system!

Metallica did a private show yesterday in Antarctica as part of a Coke Zero promotion. They performed for winners who got a 10 day cruise to Antarctica where Metallica played for them at the Carlini Station.  The gig was made even more special by the fact that Metallica had no amps or P. A.  The band, the research station scientists, the winners (Russians, South Koreans, Chinese, Polish, Chileans, Brazilians and Germans), as well as the ships crew heard the whole show through headphones!!

The show was streamed to the above named countries and you can see it below! I'm not exactly sure how this vid was uploaded but the sound is a little weird.

It's still pretty cool though, cue in to about 32:00 to skip all the announcer BS and get right to Metallicas arrival at the helipad.