The Greenland ice sheet is massive, mysterious -- and melting. Using advanced technology, scientists are revealing its secrets for the first time, and what they've found is amazing: hidden under the ice sheet is a vast aquifer that holds a Lake Tahoe-sized volume of water from the summer melt. Does this water stay there, or does it find its way out to the ocean and contribute to global sea level rise? Join glaciologist Kristin Poinar for a trip to this frozen, forgotten land to find out.