03/28/2008 02:45 am ET Updated Nov 17, 2011

Where Explorers Go When The World's Been Mapped

The North Pole, the earth's northernmost point, sits not on land but in the middle of the Arctic Ocean. To get there, you must traverse hundreds of miles across sea ice that is, in many places, jagged with pressure ridges-towering heaps of broken ice blocks--and cut by fissures in the ice that can be so long and wide you must swim across them to stay on course. Temperatures can plummet to below -60?C. And, always, there is the danger of falling through thin ice into the deep, cold sea below.