Here is a 3D rendering of a small portion of Vatnajökull Glacier. Pretty cool.
You can see why those vikings came up with the best mythology ever. Frost giants? Totally believable when you're looking at the Vatnajökull.
Frost giants were the sworn enemy of the Norse gods, among whom were Odin, Thor and Loki. They were said to live in Jotunheim, a freezing, icy wasteland full of mountains near the sea. Iceland, in other words. Jotunheim.
There were fire giants, too, led by Surt (or Surtr), who will destroy the world some day. The volcanos of Iceland undoubtedly helped the Norse to picture the fiery realm of Muspelheim.