At about 6:00 a.m., National Geographic Explorer cruises past the mouth of Ilulissat Icefjord, north of the Arctic Circle. The entrance, or terminus, is an icy wall, a couple hundred feet tall in places. The fjord is almost straight. It was not made by any valley glacier twisting and turning like a frozen river. This fjord was made by a mighty arm of the Greenland Icecap that punched its way through mountains and valleys from Greenland’s interior to the sea. We dock in Ilulissat. It is a pretty town, but our day is built around Ilulissat Icefjord, a UNESCO World Heritage Site. The iceberg parent is Sermeq Kujalleq (formerly Jakobshavn Glacier), the most active glacier in the world, north of Antarctica. Today, we explore the icefjord from the land and the sea.