For me, among the most spectacular sights in the Arctic are calving glaciers. Here, large chunks of the terminal face of Lilliehöökbreen in Spitsbergen fall into the sea, startling a flock of Kittiwakes into flight.
The sound is immense, and always reaches you a second or two after the initial impact.
Walrus aren't very confident on land - they're far too heavy and awkward to move well. In the water, it's a different story, and their curiosity will sometimes bring them very close to visiting zodiacs.